diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 484932b539eb7..b8c036f5724dd 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -111,6 +111,9 @@ fn syntax_expander_table() -> hashmap<~str, syntax_extension> {
                             builtin(ext::source_util::expand_mod));
     syntax_expanders.insert(~"proto",
                             builtin_item_tt(ext::pipes::expand_proto));
+    syntax_expanders.insert(
+        ~"trace_macros",
+        builtin_expr_tt(ext::trace_macros::expand_trace_macros));
     return syntax_expanders;
 }
 
@@ -136,6 +139,8 @@ trait ext_ctxt {
     fn span_bug(sp: span, msg: ~str) -> !;
     fn bug(msg: ~str) -> !;
     fn next_id() -> ast::node_id;
+    pure fn trace_macros() -> bool;
+    fn set_trace_macros(x: bool);
 }
 
 fn mk_ctxt(parse_sess: parse::parse_sess,
@@ -143,7 +148,8 @@ fn mk_ctxt(parse_sess: parse::parse_sess,
     type ctxt_repr = {parse_sess: parse::parse_sess,
                       cfg: ast::crate_cfg,
                       mut backtrace: expn_info,
-                      mut mod_path: ~[ast::ident]};
+                      mut mod_path: ~[ast::ident],
+                      mut trace_mac: bool};
     impl ctxt_repr: ext_ctxt {
         fn codemap() -> codemap { self.parse_sess.cm }
         fn parse_sess() -> parse::parse_sess { self.parse_sess }
@@ -199,12 +205,19 @@ fn mk_ctxt(parse_sess: parse::parse_sess,
         fn next_id() -> ast::node_id {
             return parse::next_node_id(self.parse_sess);
         }
+        pure fn trace_macros() -> bool {
+            self.trace_mac
+        }
+        fn set_trace_macros(x: bool) {
+            self.trace_mac = x
+        }
     }
     let imp : ctxt_repr = {
         parse_sess: parse_sess,
         cfg: cfg,
         mut backtrace: none,
-        mut mod_path: ~[]
+        mut mod_path: ~[],
+        mut trace_mac: false
     };
     return imp as ext_ctxt
 }
diff --git a/src/libsyntax/ext/trace_macros.rs b/src/libsyntax/ext/trace_macros.rs
new file mode 100644
index 0000000000000..d4f1493169f18
--- /dev/null
+++ b/src/libsyntax/ext/trace_macros.rs
@@ -0,0 +1,27 @@
+import codemap::span;
+import ext::base::ext_ctxt;
+import ast::tt_delim;
+import parse::lexer::{new_tt_reader, reader};
+import parse::parser::{parser, SOURCE_FILE};
+import parse::common::parser_common;
+
+fn expand_trace_macros(cx: ext_ctxt, sp: span,
+                       tt: ~[ast::token_tree]) -> base::mac_result
+{
+    let sess = cx.parse_sess();
+    let cfg = cx.cfg();
+    let tt_rdr = new_tt_reader(cx.parse_sess().span_diagnostic,
+                               cx.parse_sess().interner, none, tt);
+    let rdr = tt_rdr as reader;
+    let rust_parser = parser(sess, cfg, rdr.dup(), SOURCE_FILE);
+
+    let arg = rust_parser.parse_ident();
+    match arg {
+      @~"true"  => cx.set_trace_macros(true),
+      @~"false" => cx.set_trace_macros(false),
+      _ => cx.span_fatal(sp, ~"trace_macros! only accepts `true` or `false`")
+    }
+    let rust_parser = parser(sess, cfg, rdr.dup(), SOURCE_FILE);
+    let result = rust_parser.parse_expr();
+    base::mr_expr(result)
+}
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 381910650749e..05db498a0221e 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -47,15 +47,17 @@ fn add_new_extension(cx: ext_ctxt, sp: span, name: ident,
     };
 
     // Given `lhses` and `rhses`, this is the new macro we create
-    fn generic_extension(cx: ext_ctxt, sp: span, _name: ident,
+    fn generic_extension(cx: ext_ctxt, sp: span, name: ident,
                          arg: ~[ast::token_tree],
                          lhses: ~[@named_match], rhses: ~[@named_match])
     -> mac_result {
 
-        //io::println(fmt!("%s! { %s }", *name,
-        //                 print::pprust::unexpanded_tt_to_str(
-        //                     ast::tt_delim(arg),
-        //                     cx.parse_sess().interner)));
+        if cx.trace_macros() {
+            io::println(fmt!("%s! { %s }", *name,
+                             print::pprust::unexpanded_tt_to_str(
+                                 ast::tt_delim(arg),
+                                 cx.parse_sess().interner)));
+        }
 
         // Which arm's failure should we report? (the one furthest along)
         let mut best_fail_spot = {lo: 0u, hi: 0u, expn_info: none};
diff --git a/src/libsyntax/syntax.rc b/src/libsyntax/syntax.rc
index 37eaef0f8a3a5..ab2a83342eb40 100644
--- a/src/libsyntax/syntax.rc
+++ b/src/libsyntax/syntax.rc
@@ -89,4 +89,6 @@ mod ext {
         mod check;
         mod liveness;
     }
+
+    mod trace_macros;
 }