diff --git a/wsdiscovery/cmdline.py b/wsdiscovery/cmdline.py
index a180eb9..9edd850 100644
--- a/wsdiscovery/cmdline.py
+++ b/wsdiscovery/cmdline.py
@@ -15,9 +15,9 @@
 
 @contextmanager
 def discovery(capture=None, unicast_num=UNICAST_UDP_REPEAT,
-              multicast_num=MULTICAST_UDP_REPEAT):
+              multicast_num=MULTICAST_UDP_REPEAT, relates_to=False):
     wsd = WSDiscovery(capture=capture, unicast_num=unicast_num,
-                      multicast_num=multicast_num)
+                      multicast_num=multicast_num, relates_to=relates_to)
     wsd.start()
     yield wsd
     wsd.stop()
@@ -54,13 +54,15 @@ def setup_logger(name, loglevel):
               show_default=True, help='Number of Unicast messages to send')
 @click.option('--multicast-num', '-mn', type=int, default=MULTICAST_UDP_REPEAT,
               show_default=True, help='Number of Multicast messages to send')
+@click.option('--relates-to', '-rt', is_flag=True,
+              help='Also use RelatesTo tag to recognize incoming messages.')
 def discover(scope, address, port, loglevel, capture, timeout, unicast_num,
-             multicast_num):
+             multicast_num, relates_to):
     "Discover services using WS-Discovery"
 
     logger = setup_logger("ws-discovery", loglevel)
 
-    with discovery(capture, unicast_num, multicast_num) as wsd:
+    with discovery(capture, unicast_num, multicast_num, relates_to) as wsd:
         scopes = [Scope(scope)] if scope else []
         svcs = wsd.searchServices(scopes=scopes, address=address, port=port,
                                   timeout=timeout)
diff --git a/wsdiscovery/threaded.py b/wsdiscovery/threaded.py
index 3276125..914b466 100644
--- a/wsdiscovery/threaded.py
+++ b/wsdiscovery/threaded.py
@@ -82,6 +82,7 @@ def __init__(self, observer):
         self._iidMap = {}
         self._observer = observer
         self._capture = observer._capture
+        self._relates_to = observer._relates_to
 
         self._seqnum = 1  # capture sequence number
         self._selector = selectors.DefaultSelector()
@@ -219,7 +220,10 @@ def _recvMessages(self):
 
             mid = env.getMessageId()
             if mid in self._knownMessageIds:
-                continue  # https://github.com/andreikop/python-ws-discovery/issues/38 # TODO
+                if self._relates_to and env.getRelatesTo() in self._knownMessageIds:
+                    pass
+                else:
+                    continue
             else:
                 if self._capture:
                     self._capture.write("NEW KNOWN MSG IDS %s\n" % (mid))
@@ -367,7 +371,8 @@ class ThreadedNetworking:
 
     def __init__(self,
                  unicast_num=UNICAST_UDP_REPEAT,
-                 multicast_num=MULTICAST_UDP_REPEAT, **kwargs):
+                 multicast_num=MULTICAST_UDP_REPEAT,
+                 relates_to=False, **kwargs):
         self._networkingThread_v4 = None
         self._networkingThread_v6 = None
         self._addrsMonitorThread_v4 = None
@@ -375,6 +380,7 @@ def __init__(self,
         self._serverStarted = False
         self._unicast_num = unicast_num
         self._multicast_num = multicast_num
+        self._relates_to = relates_to
         super().__init__(**kwargs)
 
     def _startThreads(self):