The optimal agitation rate for production of swainsonine from Metarhizium anisopliae grown in batch stirred tank reactors (2 to 20 l) was 400 rpm with a mixed hyphal and pelleted morphology where the specific swainsonine production rate was 9 x 10(-2) mg g(-1) cell dry wt h from 87 to 142 h. Culture of the fungus in a 6-l airlift reactor produced ＇loose＇ pellets and the production of swainsonine started at least 24 h earlier than in the stirred tank reactor. The final yield (5.9 mg swainsonine g(-1) cell dry wt) after 168 h in the airlift reactor was 18% less than those obtained in the stirred tank reactor with an agitation rate of 400 rpm.