The bioaccumulation and elimination of endosulfan in zebra fish (Brachydanio rerio) were investigated in a semi-static bioassay. The pesticide mean concentration in water was 0.3 mug litre-1 and the level of endosulfan residues (alpha-+beta-isomers+endosulfan sulfate) in the exposed fish at day 21 was 0.81 (+/-0.12) mug g-1 body weight. The estimated value of the bioconcentration factor (BCF) was 2650 (+/-441), the total endosulfan residues being eliminated with a biological half-life of four days. Histopathological studies showed predominantly lipid accumulation in the liver and necrotic focus in the gills of exposed fish.363207211