diff --git a/tests/latency.py b/tests/latency.py
new file mode 100644
index 0000000..3cf8c5d
--- /dev/null
+++ b/tests/latency.py
@@ -0,0 +1,107 @@
+"""
+Latency tests
+
+These tests are mostly helpful for finding an optimal value for the
+--default-negative-timeout option. If this value is too large it will
+unnecessarily some down testing, but if it is too small then tests
+may pass when they should have failed.
+
+Most of this latency is caused by OFTest. Actual switch latency should be just
+a few microseconds, but OFTest can add milliseconds on top of that.
+"""
+
+import logging
+import unittest
+import time
+
+from oftest import config
+import ofp
+import oftest.base_tests as base_tests
+
+from oftest.testutils import *
+
+class DataplaneLatency(base_tests.SimpleDataPlane):
+    """
+    Measure and assert dataplane latency
+
+    All packets must arrive within the default timeout, and 90% must
+    arrive within the default negative timeout.
+    """
+    def runTest(self):
+        in_port, out_port = openflow_ports(2)
+
+        delete_all_flows(self.controller)
+
+        pkt = str(simple_tcp_packet())
+
+        request = ofp.message.flow_add(
+            match=ofp.match(wildcards=ofp.OFPFW_ALL),
+            buffer_id=0xffffffff,
+            actions=[ofp.action.output(out_port)])
+        
+        self.controller.message_send(request)
+        do_barrier(self.controller)
+
+        latencies = []
+        for i in xrange(0, 1000):
+            start_time = time.time()
+            self.dataplane.send(in_port, pkt)
+            verify_packet(self, pkt, out_port)
+            end_time = time.time()
+            latencies.append(end_time - start_time)
+
+        latencies.sort()
+        
+        latency_min = latencies[0]
+        latency_90 = latencies[int(len(latencies)*0.9)]
+        latency_max = latencies[-1]
+
+        logging.debug("Minimum latency: %f ms", latency_min * 1000.0)
+        logging.debug("90%% latency: %f ms", latency_90 * 1000.0)
+        logging.debug("Maximum latency: %f ms", latency_max * 1000.0)
+
+        self.assertGreater(config["default_timeout"], latency_max)
+        self.assertGreater(config["default_negative_timeout"], latency_90)
+
+class PktinLatency(base_tests.SimpleDataPlane):
+    """
+    Measure and assert packet-in latency
+
+    All packet-ins must arrive within the default timeout, and 90% must
+    arrive within the default negative timeout.
+    """
+    def runTest(self):
+        in_port, = openflow_ports(1)
+
+        delete_all_flows(self.controller)
+
+        pkt = str(simple_tcp_packet())
+
+        request = ofp.message.flow_add(
+            match=ofp.match(wildcards=ofp.OFPFW_ALL),
+            buffer_id=0xffffffff,
+            actions=[ofp.action.output(ofp.OFPP_CONTROLLER)])
+        
+        self.controller.message_send(request)
+        do_barrier(self.controller)
+
+        latencies = []
+        for i in xrange(0, 1000):
+            start_time = time.time()
+            self.dataplane.send(in_port, pkt)
+            verify_packet_in(self, pkt, in_port, ofp.OFPR_ACTION)
+            end_time = time.time()
+            latencies.append(end_time - start_time)
+
+        latencies.sort()
+        
+        latency_min = latencies[0]
+        latency_90 = latencies[int(len(latencies)*0.9)]
+        latency_max = latencies[-1]
+
+        logging.debug("Minimum latency: %f ms", latency_min * 1000.0)
+        logging.debug("90%% latency: %f ms", latency_90 * 1000.0)
+        logging.debug("Maximum latency: %f ms", latency_max * 1000.0)
+
+        self.assertGreater(config["default_timeout"], latency_max)
+        self.assertGreater(config["default_negative_timeout"], latency_90)