diff --git a/examples/multiplex/svc1.c b/examples/multiplex/svc1.c
index 12f06203f3369e5532e6556776d3e566f725cd7c..0ee59a8bc11b087a6c758d366de124ec0d56c61d 100644
--- a/examples/multiplex/svc1.c
+++ b/examples/multiplex/svc1.c
@@ -134,11 +134,7 @@ int svc1_register(margo_instance_id mid, ABT_pool pool, uint32_t mplex_id)
         return(ret);
     }
     
-    /* TODO: for each function:
-     * - register with margo
-     *   - this will put into hash table in mid that can map <id,mplex_id> to
-     *     <pool>, checking for duplicate first
-     *
+    /* TODO: 
      * - elsewhere:
      *   - new variant of DEFINE_MARGO_RPC_HANDLER that:
      *     - looks up registered margo thing
diff --git a/src/margo.c b/src/margo.c
index d5c4daf88874e9a06a8e9b540bfca542e21dc4a7..6bace3b2a661b27f1fb7f9a93b9a6a3a15d36b3e 100644
--- a/src/margo.c
+++ b/src/margo.c
@@ -16,9 +16,23 @@
 #include "margo.h"
 #include "margo-timer.h"
 #include "utlist.h"
+#include "uthash.h"
 
 #define MERCURY_PROGRESS_TIMEOUT_UB 100 /* 100 milliseconds */
 
+struct mplex_key
+{
+    hg_id_t id;
+    uint32_t mplex_id;
+};
+
+struct mplex_element
+{
+    struct mplex_key key;
+    ABT_pool pool;
+    UT_hash_handle hh;
+};
+
 struct margo_instance
 {
     /* provided by caller */
@@ -43,6 +57,9 @@ struct margo_instance
     ABT_cond finalize_cond;
 
     int table_index;
+
+    /* hash table to track multiplexed rpcs registered with margo */
+    struct mplex_element *mplex_table;
 };
 
 struct margo_handler_mapping
@@ -787,5 +804,24 @@ static int margo_xstream_is_in_progress_pool(margo_instance_id mid)
 
 int margo_register_mplex(margo_instance_id mid, hg_id_t id, uint32_t mplex_id, ABT_pool pool)
 {
-    return(-1);
+    struct mplex_key key;
+    struct mplex_element *element;
+
+    memset(&key, 0, sizeof(key));
+    key.id = id;
+    key.mplex_id = mplex_id;
+
+    HASH_FIND(hh, mid->mplex_table, &key, sizeof(key), element);
+    if(element)
+        return(0);
+
+    element = malloc(sizeof(*element));
+    if(!element)
+        return(-1);
+    element->key = key;
+    element->pool = pool;
+
+    HASH_ADD(hh, mid->mplex_table, key, sizeof(key), element);
+
+    return(0);
 }