diff -r eb26255e11f1 Lib/http/client.py
--- a/Lib/http/client.py	Wed Jan 28 11:06:04 2015 +0200
+++ b/Lib/http/client.py	Wed Jan 28 07:22:17 2015 -0800
@@ -776,6 +776,9 @@
             if line in (b'\r\n', b'\n', b''):
                 break
 
+            if self.debuglevel > 0:
+                print('header:', line.decode())
+
     def connect(self):
         """Connect to the host and port specified in __init__."""
         self.sock = self._create_connection(
diff -r eb26255e11f1 Lib/test/test_httplib.py
--- a/Lib/test/test_httplib.py	Wed Jan 28 11:06:04 2015 +0200
+++ b/Lib/test/test_httplib.py	Wed Jan 28 07:22:17 2015 -0800
@@ -1320,6 +1320,25 @@
         self.assertIn(b'CONNECT destination.com', self.conn.sock.data)
         self.assertIn(b'Host: destination.com', self.conn.sock.data)
 
+    def test_tunnel_debuglog(self):
+        expected_header = 'X-Dummy: 1'
+        response_text = 'HTTP/1.0 200 OK\r\n{}\r\n\r\n'.format(expected_header)
+
+        def create_connection(address, timeout=None, source_address=None):
+            return FakeSocket(
+                response_text, host=address[0], port=address[1])
+
+        conn = client.HTTPConnection('proxy.com')
+        conn._create_connection = create_connection
+        conn.set_debuglevel(1)
+
+        conn.set_tunnel('destination.com')
+
+        with support.captured_stdout() as output:
+            conn.request('PUT', '/', '')
+
+        lines = output.getvalue().splitlines()
+        self.assertIn('header: {}'.format(expected_header), lines)
 
 
 @support.reap_threads