diff --git a/stdlib/hashtbl.ml b/stdlib/hashtbl.ml
index e77311446..dbcdcf770 100644
--- a/stdlib/hashtbl.ml
+++ b/stdlib/hashtbl.ml
@@ -5,7 +5,7 @@
 (*            Xavier Leroy, projet Cristal, INRIA Rocquencourt         *)
 (*                                                                     *)
 (*  Copyright 1996 Institut National de Recherche en Informatique et   *)
-(*  Automatique.  Distributed only by permission.                      *)
+(*  en Automatique.  Distributed only by permission.                   *)
 (*                                                                     *)
 (***********************************************************************)
 
@@ -104,6 +104,14 @@ let find_all h key =
       if k = key then d :: find_in_bucket rest else find_in_bucket rest in
   find_in_bucket h.data.((hash_param 10 100 key) mod (Array.length h.data))
 
+let mem h key =
+  let rec mem_in_bucket = function
+  | Empty ->
+      false
+  | Cons(k, d, rest) ->
+      k = key || mem_in_bucket rest in
+  mem_in_bucket h.data.((hash_param 10 100 key) mod (Array.length h.data))
+
 let iter f h =
   let rec do_bucket = function
       Empty ->
@@ -134,6 +142,7 @@ module type S =
     val remove: 'a t -> key -> unit
     val find: 'a t -> key -> 'a
     val find_all: 'a t -> key -> 'a list
+    val mem : 'a t -> key -> bool
     val iter: (key -> 'a -> unit) -> 'a t -> unit
   end
 
@@ -193,5 +202,14 @@ module Make(H: HashedType): (S with type key = H.t) =
           else find_in_bucket rest in
       find_in_bucket h.data.((H.hash key) mod (Array.length h.data))
 
+    let mem h key =
+      let rec mem_in_bucket = function
+      | Empty ->
+          false
+      | Cons(k, d, rest) ->
+          H.equal k key || mem_in_bucket rest in
+      mem_in_bucket h.data.((hash_param 10 100 key) mod (Array.length h.data))
+
+
     let iter = iter
   end
diff --git a/stdlib/hashtbl.mli b/stdlib/hashtbl.mli
index d34804e8d..57574aa9a 100644
--- a/stdlib/hashtbl.mli
+++ b/stdlib/hashtbl.mli
@@ -5,7 +5,7 @@
 (*            Xavier Leroy, projet Cristal, INRIA Rocquencourt         *)
 (*                                                                     *)
 (*  Copyright 1996 Institut National de Recherche en Informatique et   *)
-(*  Automatique.  Distributed only by permission.                      *)
+(*  en Automatique.  Distributed only by permission.                   *)
 (*                                                                     *)
 (***********************************************************************)
 
@@ -47,6 +47,9 @@ val find_all : ('a, 'b) t -> 'a -> 'b list
            The current binding is returned first, then the previous
            bindings, in reverse order of introduction in the table. *)
 
+val mem :  ('a, 'b) t -> 'a -> bool
+        (* [Hashtbl.mem tbl x] checks if [x] is bound in [tbl]. *)
+
 val remove : ('a, 'b) t -> 'a -> unit
         (* [Hashtbl.remove tbl x] removes the current binding of [x] in [tbl],
            restoring the previous binding if it exists.
@@ -90,6 +93,7 @@ module type S =
     val remove: 'a t -> key -> unit
     val find: 'a t -> key -> 'a
     val find_all: 'a t -> key -> 'a list
+    val mem: 'a t -> key -> bool
     val iter: (key -> 'a -> unit) -> 'a t -> unit
   end