The effects of benzene hexachloride (BHC), an organochlorine pesticide, on cell growth and phosphatase activities were studied in the growing and developing stages of cells of the cellular slime mould Dictyostelium discoideum exposed to BHC (containing alpha-, beta-, delta- and gamma-isomers) at concentrations of > or = 60 micrograms ml-1. A significant increase in acid and alkaline phosphatase activities was recorded in both growing and differentiating Dictyostelium cells treated with different doses (> or = 60 micrograms/ml) of BHC. The cytotoxicity of BHC has been correlated with the stimulation of acid and alkaline phosphatase activities of this organism.