To diversify or not to diversify, to focus or not to focus. Biotech companies with more than one technology may be accused of being spread too thin, while those with only one may be criticized as too narrow.

But instead of thinking about the issue in static terms, it may be more helpful to think about it longitudinally. That's what Cell Genesys Inc. has done, announcing last week that it is spinning off its human monoclonal antibody technology into a wholly owned subsidiary, Abgenix Inc.