ò etc.

Can someone explain me why Mozilla (1.2a as well as Firebird 0.6)
gives me the following error if I try to load a DocBook XML document:

XML Parsing Error: undefined entity
Location: file:///home/mw/work/tex-refs/tex-refs.xml
Line Number 4427, Column 19: <emphasis>&ograve;</emphasis></simpara>

... and even better, what should I do to avoid this kind of error
(there a quite a few characters like &ograve;, &oacute;, &ocirc;,
etc. in my document).

Michael
PS: applying the standard XSL stylesheets on the same document
    generates HTML without any problems.
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