diff --git a/scrapy/http/request/form.py b/scrapy/http/request/form.py
index 55e5ea1fa..e7a654ab9 100644
--- a/scrapy/http/request/form.py
+++ b/scrapy/http/request/form.py
@@ -22,6 +22,8 @@ def _unicode_to_str(string, encoding):
 
 class FormRequest(Request):
 
+    __slots__ = ()
+
     def __init__(self, *args, **kwargs):
         formdata = kwargs.pop('formdata', None)
         Request.__init__(self, *args, **kwargs)
diff --git a/scrapy/http/response/html.py b/scrapy/http/response/html.py
index 013e0805b..66e9124b5 100644
--- a/scrapy/http/response/html.py
+++ b/scrapy/http/response/html.py
@@ -12,6 +12,8 @@ from scrapy.utils.python import memoizemethod
 
 class HtmlResponse(TextResponse):
 
+    __slots__ = ()
+
     _template = r'''%s\s*=\s*["']?\s*%s\s*["']?'''
 
     _httpequiv_re = _template % ('http-equiv', 'Content-Type')
diff --git a/scrapy/http/response/xml.py b/scrapy/http/response/xml.py
index d14aaa80f..760ad33b9 100644
--- a/scrapy/http/response/xml.py
+++ b/scrapy/http/response/xml.py
@@ -12,6 +12,8 @@ from scrapy.utils.python import memoizemethod
 
 class XmlResponse(TextResponse):
 
+    __slots__ = ()
+
     _template = r'''%s\s*=\s*["']?\s*%s\s*["']?'''
     _encoding_re  = _template % ('encoding', r'(?P<charset>[\w-]+)')
     XMLDECL_RE  = re.compile(r'<\?xml\s.*?%s' % _encoding_re, re.I)
diff --git a/scrapy/link.py b/scrapy/link.py
index 1844da1da..657fa541b 100644
--- a/scrapy/link.py
+++ b/scrapy/link.py
@@ -10,7 +10,7 @@ class Link(object):
     At the moment, it contains just the url and link text.
     """
 
-    __slots__ = 'url', 'text'
+    __slots__ = ['url', 'text']
 
     def __init__(self, url, text=''):
         self.url = url
diff --git a/scrapy/tests/test_http_headers.py b/scrapy/tests/test_http_headers.py
index 3d4136c09..871a987ca 100644
--- a/scrapy/tests/test_http_headers.py
+++ b/scrapy/tests/test_http_headers.py
@@ -1,4 +1,5 @@
 import unittest
+import weakref
 import copy
 
 from scrapy.http import Headers
@@ -103,3 +104,8 @@ class HeadersTest(unittest.TestCase):
         self.assertEqual(h1.getlist('header1'), ['value1'])
         self.assertEqual(h1.getlist('header2'), ['value2', 'value3'])
 
+    def test_slots(self):
+        """Check that classes are using slots and are weak-referenceable"""
+        x = Headers({})
+        assert not hasattr(x, '__dict__'), "%s does not use __slots__" % \
+            x.__class__.__name__
diff --git a/scrapy/tests/test_http_request.py b/scrapy/tests/test_http_request.py
index ac6ee18dc..ecf94100a 100644
--- a/scrapy/tests/test_http_request.py
+++ b/scrapy/tests/test_http_request.py
@@ -1,5 +1,6 @@
 import unittest
 import cgi
+import weakref
 from cStringIO import StringIO
 from urlparse import urlparse
 
@@ -166,6 +167,14 @@ class RequestTest(unittest.TestCase):
         self.assertEqual(r4.meta, {})
         assert r4.dont_filter is False
 
+    def test_weakref_slots(self):
+        """Check that classes are using slots and are weak-referenceable"""
+        for cls in [Request, FormRequest]:
+            x = cls('http://www.example.com')
+            weakref.ref(x)
+            assert not hasattr(x, '__dict__'), "%s does not use __slots__" % \
+                x.__class__.__name__
+
 
 class FormRequestTest(unittest.TestCase):
 
@@ -299,6 +308,5 @@ class XmlRpcRequestTest(unittest.TestCase):
         self.assertEqual(r1.body, r2.body)
 
 
-
 if __name__ == "__main__":
     unittest.main()
diff --git a/scrapy/tests/test_http_response.py b/scrapy/tests/test_http_response.py
index d60d43328..ccf5ae6cc 100644
--- a/scrapy/tests/test_http_response.py
+++ b/scrapy/tests/test_http_response.py
@@ -1,4 +1,6 @@
 import unittest
+import weakref
+
 from scrapy.http import Response, TextResponse, HtmlResponse, XmlResponse, Headers
 
 class ResponseTest(unittest.TestCase):
@@ -201,6 +203,14 @@ class ResponseTest(unittest.TestCase):
         self._assert_response_values(r5, 'iso-8859-1', body)
         self._assert_response_values(r6, 'utf-8', body2)
 
+    def test_weakref_slots(self):
+        """Check that classes are using slots and are weak-referenceable"""
+        for cls in [Response, TextResponse, XmlResponse, HtmlResponse]:
+            x = cls('http://www.example.com')
+            weakref.ref(x)
+            assert not hasattr(x, '__dict__'), "%s does not use __slots__" % \
+                x.__class__.__name__
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/scrapy/tests/test_xpath.py b/scrapy/tests/test_xpath.py
index 08032d9b3..582932132 100644
--- a/scrapy/tests/test_xpath.py
+++ b/scrapy/tests/test_xpath.py
@@ -1,10 +1,12 @@
 import re
 import unittest
+import weakref
 
 import libxml2
 
 from scrapy.http import TextResponse, HtmlResponse, XmlResponse
-from scrapy.xpath.selector import XmlXPathSelector, HtmlXPathSelector
+from scrapy.xpath.selector import XmlXPathSelector, HtmlXPathSelector, \
+    XPathSelector
 from scrapy.xpath.document import Libxml2Document
 from scrapy.utils.test import libxml2debug
 
@@ -239,6 +241,15 @@ class XPathSelectorTestCase(unittest.TestCase):
             u'\n  ',
             u'\n  pff\n'])
 
+    @libxml2debug
+    def test_weakref_slots(self):
+        """Check that classes are using slots and are weak-referenceable"""
+        for cls in [XPathSelector, HtmlXPathSelector, XmlXPathSelector]:
+            x = cls()
+            weakref.ref(x)
+            assert not hasattr(x, '__dict__'), "%s does not use __slots__" % \
+                x.__class__.__name__
+
 class Libxml2DocumentTest(unittest.TestCase):
 
     @libxml2debug
diff --git a/scrapy/utils/datatypes.py b/scrapy/utils/datatypes.py
index 094be5e0c..044bcae27 100644
--- a/scrapy/utils/datatypes.py
+++ b/scrapy/utils/datatypes.py
@@ -160,6 +160,9 @@ class SiteNode(object):
 
 
 class CaselessDict(dict):
+
+    __slots__ = ()
+
     def __init__(self, seq=None):
         super(CaselessDict, self).__init__()
         if seq:
diff --git a/scrapy/xpath/selector.py b/scrapy/xpath/selector.py
index 1e0483600..f7d579a12 100644
--- a/scrapy/xpath/selector.py
+++ b/scrapy/xpath/selector.py
@@ -140,9 +140,10 @@ class XPathSelectorList(list):
 
 class XmlXPathSelector(XPathSelector):
     """XPathSelector for XML content"""
+    __slots__ = ()
     _get_libxml2_doc = staticmethod(xmlDoc_from_xml)
 
-
 class HtmlXPathSelector(XPathSelector):
     """XPathSelector for HTML content"""
+    __slots__ = ()
     _get_libxml2_doc = staticmethod(xmlDoc_from_html)