Metarhizium anisopliae was cultured batchwise in stirred-tank reactors using complex media selected for the enhanced production of swainsonine. A swainsonine concentration of 40 mg l(-1) produced at 170 h was more than double that obtained from shaken-flask cultures in the same medium after the same period of time. When conventional Rushton turbine impellers were employed, detrimental surface cake formation was observed after 90 h in the fermenters, resulting in nonhomogenous cultures and reduced productivity. Improved culture homogeneity and swainsonine production were achieved through alteration of the impeller type and position in the reactor. Further improvements were obtained by the adoption of controlled aeration strategies.