diff --git a/scrapy/selector/lxmldocument.py b/scrapy/selector/lxmldocument.py
new file mode 100644
index 000000000..065ce222b
--- /dev/null
+++ b/scrapy/selector/lxmldocument.py
@@ -0,0 +1,31 @@
+"""
+This module contains a simple class (LxmlDocument) which provides cache and
+garbage collection to lxml element tree documents.
+"""
+
+import weakref
+from lxml import etree
+from scrapy.utils.trackref import object_ref
+
+
+def _factory(response, parser_cls):
+    url = response.url
+    body = response.body_as_unicode().strip().encode('utf8') or '<html/>'
+    parser = parser_cls(recover=True, encoding='utf8')
+    return etree.fromstring(body, parser=parser, base_url=url)
+
+
+class LxmlDocument(object_ref):
+
+    cache = weakref.WeakKeyDictionary()
+    __slots__ = ['xmlDoc', 'xpathContext', '__weakref__']
+
+    def __new__(cls, response, parser=etree.HTMLParser):
+        cache = cls.cache.setdefault(response, {})
+        if parser not in cache:
+            obj = object_ref.__new__(cls)
+            cache[parser] = _factory(response, parser)
+        return cache[parser]
+
+    def __str__(self):
+        return "<LxmlDocument %s>" % self.root.tag
diff --git a/scrapy/selector/lxmlsel.py b/scrapy/selector/lxmlsel.py
index bb0a4e1ec..af6839474 100644
--- a/scrapy/selector/lxmlsel.py
+++ b/scrapy/selector/lxmlsel.py
@@ -9,42 +9,35 @@ from scrapy.utils.trackref import object_ref
 from scrapy.utils.python import unicode_to_str
 from scrapy.utils.decorator import deprecated
 from scrapy.http import TextResponse
+from .lxmldocument import LxmlDocument
 from .list import XPathSelectorList
 
+
 __all__ = ['HtmlXPathSelector', 'XmlXPathSelector', 'XPathSelector', \
-    'XPathSelectorList']
+           'XPathSelectorList']
+
 
 class XPathSelector(object_ref):
 
-    __slots__ = ['response', 'text', 'expr', 'namespaces', '_root', '_xpathev', \
-        '__weakref__']
+    __slots__ = ['response', 'text', 'namespaces', '_expr', '_root', '__weakref__']
     _parser = etree.HTMLParser
     _tostring_method = 'html'
 
-    def __init__(self, response=None, text=None, root=None, expr=None, namespaces=None):
-        if text:
-            self.response = TextResponse(url='about:blank', \
+    def __init__(self, response=None, text=None, namespaces=None, _root=None, _expr=None):
+        if text is not None:
+            response = TextResponse(url='about:blank', \
                 body=unicode_to_str(text, 'utf-8'), encoding='utf-8')
-        else:
-            self.response = response
-        self._root = root
-        self._xpathev = None
-        self.namespaces = namespaces
-        self.expr = expr
+        if response is not None:
+            _root = LxmlDocument(response, self._parser)
 
-    @property
-    def root(self):
-        if self._root is None:
-            url = self.response.url
-            body = self.response.body_as_unicode().strip().encode('utf8') or '<html/>'
-            parser = self._parser(recover=True, encoding='utf8')
-            self._root = etree.fromstring(body, parser=parser, base_url=url)
-            assert self._root is not None, 'BUG lxml selector with None root'
-        return self._root
+        self.namespaces = namespaces
+        self.response = response
+        self._root = _root
+        self._expr = _expr
 
     def select(self, xpath):
         try:
-            xpathev = self.root.xpath
+            xpathev = self._root.xpath
         except AttributeError:
             return XPathSelectorList([])
 
@@ -56,7 +49,7 @@ class XPathSelector(object_ref):
         if type(result) is not list:
             result = [result]
 
-        result = [self.__class__(root=x, expr=xpath, namespaces=self.namespaces)
+        result = [self.__class__(_root=x, _expr=xpath, namespaces=self.namespaces)
                   for x in result]
         return XPathSelectorList(result)
 
@@ -65,15 +58,15 @@ class XPathSelector(object_ref):
 
     def extract(self):
         try:
-            return etree.tostring(self.root, method=self._tostring_method, \
+            return etree.tostring(self._root, method=self._tostring_method, \
                 encoding=unicode)
         except (AttributeError, TypeError):
-            if self.root is True:
+            if self._root is True:
                 return u'1'
-            elif self.root is False:
+            elif self._root is False:
                 return u'0'
             else:
-                return unicode(self.root)
+                return unicode(self._root)
 
     def register_namespace(self, prefix, uri):
         if self.namespaces is None:
@@ -85,7 +78,7 @@ class XPathSelector(object_ref):
 
     def __str__(self):
         data = repr(self.extract()[:40])
-        return "<%s xpath=%r data=%s>" % (type(self).__name__, self.expr, data)
+        return "<%s xpath=%r data=%s>" % (type(self).__name__, self._expr, data)
 
     __repr__ = __str__
 
diff --git a/scrapy/tests/test_selector_lxml.py b/scrapy/tests/test_selector_lxml.py
index 8050a2758..c8eca9679 100644
--- a/scrapy/tests/test_selector_lxml.py
+++ b/scrapy/tests/test_selector_lxml.py
@@ -2,35 +2,40 @@
 Selectors tests, specific for lxml backend
 """
 
-from scrapy.http import TextResponse, XmlResponse
-has_lxml = True
-try:
-    from scrapy.selector.lxmlsel import XmlXPathSelector, HtmlXPathSelector, \
-        XPathSelector
-except ImportError:
-    has_lxml = False
-from scrapy.utils.test import libxml2debug
+import unittest
 from scrapy.tests import test_selector
+from scrapy.http import TextResponse, HtmlResponse
+from scrapy.selector.lxmldocument import LxmlDocument
+from scrapy.selector.lxmlsel import XmlXPathSelector, HtmlXPathSelector, XPathSelector
+
 
 class LxmlXPathSelectorTestCase(test_selector.XPathSelectorTestCase):
 
-    if has_lxml:
-        xs_cls = XPathSelector
-        hxs_cls = HtmlXPathSelector
-        xxs_cls = XmlXPathSelector
-    else:
-        skip = "lxml not available"
+    xs_cls = XPathSelector
+    hxs_cls = HtmlXPathSelector
+    xxs_cls = XmlXPathSelector
 
-    # XXX: this test was disabled because lxml behaves inconsistently when
-    # handling null bytes between different 2.2.x versions, but it may be due
-    # to differences in libxml2 too. it's also unclear what should be the
-    # proper behaviour (pablo - 26 oct 2010)
-    #@libxml2debug
-    #def test_null_bytes(self):
-    #    hxs = HtmlXPathSelector(text='<root>la\x00la</root>')
-    #    self.assertEqual(hxs.extract(),
-    #                     u'<html><body><root>la</root></body></html>')
-    #
-    #    xxs = XmlXPathSelector(text='<root>la\x00la</root>')
-    #    self.assertEqual(xxs.extract(),
-    #                     u'<root>la</root>')
+
+class Libxml2DocumentTest(unittest.TestCase):
+
+    def test_caching(self):
+        r1 = HtmlResponse('http://www.example.com', body='<html><head></head><body></body></html>')
+        r2 = r1.copy()
+
+        doc1 = LxmlDocument(r1)
+        doc2 = LxmlDocument(r1)
+        doc3 = LxmlDocument(r2)
+
+        # make sure it's cached
+        assert doc1 is doc2
+        assert doc1 is not doc3
+
+        # don't leave documents in memory to avoid wrong libxml2 leaks reports
+        del doc1, doc2, doc3
+
+    def test_null_char(self):
+        # make sure bodies with null char ('\x00') don't raise a TypeError exception
+        self.body_content = 'test problematic \x00 body'
+        response = TextResponse('http://example.com/catalog/product/blabla-123',
+                            headers={'Content-Type': 'text/plain; charset=utf-8'}, body=self.body_content)
+        LxmlDocument(response)