diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1249,15 +1249,41 @@
         pass
     return baseset(datarepr=('<max %r, %r>', subset, os))
 
-@predicate('merge()', safe=True)
+@predicate('merge(withbranch)', safe=True)
 def merge(repo, subset, x):
-    """Changeset is a merge changeset.
+    """Changeset is a merge changeset
+
+    All merge revisions are returned by default. If a "withbranch"
+    pattern is provided only merges with (i.e. whose second parent
+    belongs to) those branches that match the pattern will be returned.
+    The simplest pattern is the name of a single branch. It is also
+    possible to specify a regular expression by starting the pattern
+    with "re:". This can be used to match more than one branch
+    (e.g. "re:branch1|branch2").
     """
     # i18n: "merge" is a keyword
-    getargs(x, 0, 0, _("merge takes no arguments"))
+    args = getargsdict(x, 'merge', 'withbranch')
+    withbranch = ''
+    if 'withbranch' in args:
+        withbranch = getstring(args['withbranch'],
+                               _('withbranch argument must be a string'))
+        kind, branchname, branchmatcher = stringutil.stringmatcher(withbranch)
     cl = repo.changelog
-    return subset.filter(lambda r: cl.parentrevs(r)[1] != -1,
-                         condrepr='<merge>')
+    # create the function that will be used to filter the subset
+    if withbranch:
+        # matchfn is a function that returns true when a revision
+        # is a merge and the second parent belongs to a branch that
+        # matches the withbranch pattern (which can be a literal or a regex)
+        if kind == 'literal':
+            matchfn = lambda r: (cl.parentrevs(r)[1] != -1
+                                 and repo[r].p2().branch() == withbranch)
+        else:
+            matchfn = lambda r: (cl.parentrevs(r)[1] != -1
+                                 and branchmatcher(repo[r].p2().branch()))
+    else:
+        # matchfn is a function that returns true when a revision is a merge
+        matchfn = lambda r: cl.parentrevs(r)[1] != -1
+    return subset.filter(matchfn, condrepr='<merge>')
 
 @predicate('branchpoint()', safe=True)
 def branchpoint(repo, subset, x):