The effect of an organochlorine pesticide benzene hexachloride (containing alpha, beta, gamma and delta isomers) on the phagocytic activity of the vegetative cells of Dictyostelium discoideum was investigated. Benzene hexachloride (BHC) at concentrations of 60 ppm and above inhibited the phagocytic activity as revealed by 3H-labelled E. coli uptake. The BHC treated cells also showed smaller and delayed plaque formation. Interactions of lipophilic pesticide with the hydrophobic cell surface presumably alters the receptor mediated phagocytosis of Dictyostelium amoebae.