diff --git a/rs-tests.rkt b/rs-tests.rkt
index 9601a08..a8231ae 100644
--- a/rs-tests.rkt
+++ b/rs-tests.rkt
@@ -5,8 +5,12 @@
 (require typed/rackunit "rs.rkt")
 
 (test-case "Basic definitions"
-  (let ([r (reaction (set 'a) (set 'b) (set 'c))]
-        [s1 (set 'a 'c)]
-        [s2 (set 'a 'b)])
-    (check-true (enabled? r s1))
-    (check-false (enabled? r s2))))
+  (let* ([r1 (reaction (set 'x) (set 'y) (set 'z))]
+         [r2 (reaction (set 'x) (set) (set 'y))]
+         [rs (make-immutable-hash (list (cons 'a r1) (cons 'b r2)))]
+         [s1 (set 'x 'z)]
+         [s2 (set 'x 'y)])
+    (check-true (enabled? r1 s1))
+    (check-false (enabled? r1 s2))
+    (check-equal? (list-enabled rs s1) '(a b))
+    (check-equal? (list-enabled rs s2) '(b))))
diff --git a/rs.rkt b/rs.rkt
index 50e9e53..a9af363 100644
--- a/rs.rkt
+++ b/rs.rkt
@@ -10,7 +10,7 @@
  ;; Type names
  Species ReactionSystem
  ;; Functions
- enabled?)
+ enabled? list-enabled)
 
 ;;; =================
 ;;; Basic definitions
@@ -35,3 +35,10 @@
 ;;; A reaction system is a dictionary mapping reaction names to
 ;;; reactions.
 (define-type ReactionSystem (HashTable Symbol reaction))
+
+;;; Returns the list of reaction names enabled on a given set.
+(: list-enabled (-> ReactionSystem (Setof Symbol) (Listof Symbol)))
+(define (list-enabled rs s)
+  (for/list ([(name reaction) (in-hash rs)]
+             #:when (enabled? reaction s))
+    name))