diff --git a/README.md b/README.md
index f4a16ffc1..1ae3834e8 100644
--- a/README.md
+++ b/README.md
@@ -462,22 +462,67 @@ Net::HTTP.get('www.something.com', '/')    # ===> Failure
 Net::HTTP.get('localhost:9887', '/')    # ===> Allowed. Perhaps to Selenium?
 ```
 
-### External requests can be disabled while allowing any hostname or port or parts thereof
+### External requests can be disabled while allowing specific requests
+
+Allowed requests can be specified in a number of ways.
+
+With a `String` specifying a host name:
+
+```ruby
+WebMock.disable_net_connect!(:allow => 'www.example.org')
+
+RestClient.get('www.something.com', '/')    # ===> Failure
+RestClient.get('www.example.org', '/')      # ===> Allowed
+RestClient.get('www.example.org:8080', '/') # ===> Allowed
+```
+
+With a `String` specifying a host name and a port:
 
 ```ruby
-WebMock.disable_net_connect!(:allow => "www.example.org:8080")
+WebMock.disable_net_connect!(:allow => 'www.example.org:8080')
 
 RestClient.get('www.something.com', '/')    # ===> Failure
+RestClient.get('www.example.org', '/')      # ===> Failure
+RestClient.get('www.example.org:8080', '/') # ===> Allowed
+```
+
+With a `Regexp` matching the URI:
+
+```ruby
+WebMock.disable_net_connect!(:allow => %r{ample.org/foo})
 
-RestClient.get('www.example.org', '/')    # ===> Failure.
+RestClient.get('www.example.org', '/foo/bar') # ===> Allowed
+RestClient.get('sample.org', '/foo')          # ===> Allowed
+RestClient.get('sample.org', '/bar')          # ===> Failure
+```
 
-RestClient.get('www.example.org:8080', '/')    # ===> Allowed
+With an object that responds to `#call`, receiving a `URI` object and returning a boolean:
 
-WebMock.disable_net_connect!(:allow => /ample.org/)
+```ruby
+blacklist = ['google.com', 'facebook.com', 'apple.com']
+allowed_sites = lambda{|uri|
+  blacklist.none?{|site| uri.host.include?(site) }
+}
+WebMock.disable_net_connect!(:allow => allowed_sites)
+
+RestClient.get('www.example.org', '/')  # ===> Allowed
+RestClient.get('www.facebook.com', '/') # ===> Failure
+RestClient.get('apple.com', '/')        # ===> Failure
+```
 
-WebMock.disable_net_connect!(:allow => [/ample.org/, /googl/])
+With an `Array` of any of the above:
 
-RestClient.get('www.example.org', '/')    # ===> Allowed
+```ruby
+WebMock.disable_net_connect!(:allow => [
+  lambda{|uri| uri.host.length % 2 == 0 },
+  /ample.org/,
+  'bbc.co.uk',
+])
+
+RestClient.get('www.example.org', '/') # ===> Allowed
+RestClient.get('bbc.co.uk', '/')       # ===> Allowed
+RestClient.get('bbc.com', '/')         # ===> Allowed
+RestClient.get('www.bbc.com', '/')     # ===> Failure
 ```
 
 ## Connecting on Net::HTTP.start
diff --git a/lib/webmock/webmock.rb b/lib/webmock/webmock.rb
index 444c92d79..4124be54e 100644
--- a/lib/webmock/webmock.rb
+++ b/lib/webmock/webmock.rb
@@ -72,6 +72,10 @@ def self.net_connect_explicit_allowed?(allowed, uri=nil)
     when String
       allowed == uri.host ||
       allowed == "#{uri.host}:#{uri.port}"
+    else
+      if allowed.respond_to?(:call)
+        allowed.call(uri)
+      end
     end
   end
 
diff --git a/spec/acceptance/shared/allowing_and_disabling_net_connect.rb b/spec/acceptance/shared/allowing_and_disabling_net_connect.rb
index bba21fbd6..080a8b6d1 100644
--- a/spec/acceptance/shared/allowing_and_disabling_net_connect.rb
+++ b/spec/acceptance/shared/allowing_and_disabling_net_connect.rb
@@ -88,64 +88,172 @@
       end
     end
 
-    describe "is not allowed with exception for allowed domains" do
-      let(:host_with_port){ WebMockServer.instance.host_with_port }
+    describe "is not allowed, with exceptions" do
+      describe "allowing by host string" do
+        before :each do
+          WebMock.disable_net_connect!(:allow => 'httpstat.us')
+        end
 
-      before(:each) do
-        WebMock.disable_net_connect!(:allow => ["www.example.org", "httpstat.us", host_with_port])
-      end
+        context "when the host is not allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'disallowed.example.com/foo').to_return(:body => "abc")
+            expect(http_request(:get, 'http://disallowed.example.com/foo').body).to eq("abc")
+          end
 
-      context "when the host is not allowed" do
-        it "should return stubbed response if request was stubbed" do
-          stub_request(:get, "www.example.com").to_return(:body => "abc")
-          expect(http_request(:get, "http://www.example.com/").body).to eq("abc")
+          it "should raise exception if request was not stubbed" do
+            expect {
+              http_request(:get, 'http://disallowed.example.com/')
+            }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://disallowed.example.com))
+          end
         end
 
-        it "should raise exception if request was not stubbed" do
-          expect {
-            http_request(:get, "http://www.example.com/")
-          }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://www.example.com/))
+        context "when the host is allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'httpstat.us/200').to_return(:body => "abc")
+            expect(http_request(:get, "http://httpstat.us/200").body).to eq("abc")
+          end
+
+          # WARNING: this makes a real HTTP request!
+          it "should make a real request to allowed host", :net_connect => true do
+            expect(http_request(:get, "http://httpstat.us/200").status).to eq('200')
+          end
         end
       end
 
-      context "when the host with port is not allowed" do
-        it "should return stubbed response if request was stubbed" do
-          stub_request(:get, "http://localhost:2345").to_return(:body => "abc")
-          expect(http_request(:get, "http://localhost:2345/").body).to eq("abc")
+      describe "allowing by host:port string" do
+        def replace_with_different_port(uri)
+          uri.sub(%r{:(\d+)}){|m0, m1| ':' + ($~[1].to_i + 1).to_s }
+        end
+
+        let(:allowed_host_with_port) { WebMockServer.instance.host_with_port }
+        let(:disallowed_host_with_port) { replace_with_different_port(allowed_host_with_port) }
+
+        before :each do
+          WebMock.disable_net_connect!(:allow => allowed_host_with_port)
+        end
+
+        context "when the host is not allowed" do
+          it "should return stubbed response if request was stubbed" do
+            request_url = "http://#{disallowed_host_with_port}/foo"
+            stub_request(:get, request_url).to_return(:body => "abc")
+            expect(http_request(:get, request_url).body).to eq("abc")
+          end
+
+          it "should raise exception if request was not stubbed" do
+            request_url = "http://#{disallowed_host_with_port}/foo"
+            expect {
+              http_request(:get, request_url)
+            }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET #{request_url}))
+          end
         end
 
-        it "should raise exception if request was not stubbed" do
-          expect {
-            http_request(:get, "http://localhost:2345/")
-          }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://localhost:2345/))
+        context "when the host is allowed" do
+          it "should return stubbed response if request was stubbed" do
+            request_url = "http://#{allowed_host_with_port}/foo"
+            stub_request(:get, request_url).to_return(:body => "abc")
+            expect(http_request(:get, request_url).body).to eq('abc')
+          end
+
+          it "should make a real request to allowed host", :net_connect => true do
+            request_url = "http://#{allowed_host_with_port}/foo"
+            expect(http_request(:get, request_url).status).to eq('200')
+          end
         end
       end
 
-      context "when the host is allowed" do
-        it "should raise exception if request was not stubbed" do
-          expect {
-            http_request(:get, "http://www.example.com/")
-          }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://www.example.com/))
+      describe "allowing by regular expression" do
+        before :each do
+          WebMock.disable_net_connect!(:allow => %r{httpstat})
+        end
+
+        context "when the host is not allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'disallowed.example.com/foo').to_return(:body => "abc")
+            expect(http_request(:get, 'http://disallowed.example.com/foo').body).to eq("abc")
+          end
+
+          it "should raise exception if request was not stubbed" do
+            expect {
+              http_request(:get, 'http://disallowed.example.com/')
+            }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://disallowed.example.com))
+          end
         end
 
-        it "should make a real request to allowed host", :net_connect => true do
-          expect(http_request(:get, "http://httpstat.us/200").status).to eq("200")
+        context "when the host is allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'httpstat.us/200').to_return(:body => "abc")
+            expect(http_request(:get, "http://httpstat.us/200").body).to eq("abc")
+          end
+
+          # WARNING: this makes a real HTTP request!
+          it "should make a real request to allowed host", :net_connect => true do
+            expect(http_request(:get, "http://httpstat.us/200").status).to eq('200')
+          end
         end
       end
 
-      context "when the host with port is allowed" do
-        it "should make a real request to allowed host", :net_connect => true do
-          expect(http_request(:get, "http://#{host_with_port}/").status).to eq("200")
+      describe "allowing by a callable" do
+        before :each do
+          WebMock.disable_net_connect!(:allow => lambda{|url| url.to_str.include?('httpstat') })
+        end
+
+        context "when the host is not allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'disallowed.example.com/foo').to_return(:body => "abc")
+            expect(http_request(:get, 'http://disallowed.example.com/foo').body).to eq("abc")
+          end
+
+          it "should raise exception if request was not stubbed" do
+            expect {
+              http_request(:get, 'http://disallowed.example.com/')
+            }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://disallowed.example.com))
+          end
+        end
+
+        context "when the host is allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'httpstat.us/200').to_return(:body => "abc")
+            expect(http_request(:get, "http://httpstat.us/200").body).to eq("abc")
+          end
+
+          # WARNING: this makes a real HTTP request!
+          it "should make a real request to allowed host", :net_connect => true do
+            expect(http_request(:get, "http://httpstat.us/200").status).to eq('200')
+          end
         end
       end
 
-      context "when the host is allowed but not port" do
-        it "should make a real request to allowed host", :net_connect => true do
-          expect {
-            http_request(:get, "http://localhost:123/")
-          }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://localhost:123/))
+      describe "allowing by a list of the above" do
+        before :each do
+          WebMock.disable_net_connect!(:allow => [lambda{|_| false }, %r{foobar}, 'httpstat.us'])
+        end
+
+        context "when the host is not allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'disallowed.example.com/foo').to_return(:body => "abc")
+            expect(http_request(:get, 'http://disallowed.example.com/foo').body).to eq("abc")
+          end
+
+          it "should raise exception if request was not stubbed" do
+            expect {
+              http_request(:get, 'http://disallowed.example.com/')
+            }.to raise_error(WebMock::NetConnectNotAllowedError, %r(Real HTTP connections are disabled. Unregistered request: GET http://disallowed.example.com))
+          end
+        end
+
+        context "when the host is allowed" do
+          it "should return stubbed response if request was stubbed" do
+            stub_request(:get, 'httpstat.us/200').to_return(:body => "abc")
+            expect(http_request(:get, "http://httpstat.us/200").body).to eq("abc")
+          end
+
+          # WARNING: this makes a real HTTP request!
+          it "should make a real request to allowed host", :net_connect => true do
+            expect(http_request(:get, "http://httpstat.us/200").status).to eq('200')
+          end
         end
       end
+
     end
   end
 end