diff --git a/src/GraphProperties.jl b/src/GraphProperties.jl
index 99a081f..3759d91 100644
--- a/src/GraphProperties.jl
+++ b/src/GraphProperties.jl
@@ -56,6 +56,10 @@ let
         (:NumberOfConnectedComponents, "The *number of connected components* of an undirected graph."),
         (:MinimumDegree, "The *minimum degree* among the degrees of the vertices of an undirected graph."),
         (:MaximumDegree, "The *maximum degree* among the degrees of the vertices of an undirected graph."),
+        (:MinimumIndegree, "The *minimum indegree* among the indegrees of the vertices of a directed graph."),
+        (:MaximumIndegree, "The *maximum indegree* among the indegrees of the vertices of a directed graph."),
+        (:MinimumOutdegree, "The *minimum outdegree* among the outdegrees of the vertices of a directed graph."),
+        (:MaximumOutdegree, "The *maximum outdegree* among the outdegrees of the vertices of a directed graph."),
         (:Girth, "The *girth* of a undirected graph: the length of its shortest cycle."),
         (:VertexConnectivity, "The *vertex-connectivity* of an undirected graph. Also known as the *connectivity*."),
         (:EdgeConnectivity, "The *edge-connectivity* of an undirected graph."),