Ok this is definitely not an lxml problem. Here's how you can recreate the same problem I had.. duh! If you (accidentally) use the same base_url for when loading both the xsl and xml source, there's a 50% chance that document('') will return the xml source, not the xsl source object. class Tester(object): def test(self): xsl_resolver = Resolver(fake_resolve_function) xsl_parser = etree.XMLParser(load_dtd=True) xsl_parser.resolvers.add(Resolver(resolver=xsl_resolver)) stylesheet_doc = etree.fromstring(xsl_src, xsl_parser, base_url='/carriers/view.htm') stylesheet = etree.XSLT(stylesheet_doc) xml_resolver = Resolver(fake_resolve_function) xml_parser = etree.XMLParser(load_dtd=True) xml_parser.resolvers.add(Resolver(resolver=xml_resolver)) xml_doc = etree.fromstring(xml_src, xml_parser, base_url='/carriers/view.htm') return str(stylesheet(xml_doc)) -- Brad Clements, bkc@murkworks.com (315)268-1000 http://www.murkworks.com AOL-IM: BKClements