This paper reports the histological analysis of various organs of Mugil sp., Cyprinus carpio and Barbus sp. after an accidental discharge of lindane (?-Hexachloro-cyclohexane - ?-HCH-) into the Barbate River (Cádiz, SW Spain). Histopathological alterations of gills, liver and kidney were detected. Fusion of the secondary lamella, increased raising of the branchial epithelium and intraepithelial edema in gills, reduction of the diameter of the hepatocytes and, in advanced cases, cellular vacuolisation with hypertrophy of the hepatocytes in liver, as well as tubular necrosis, desquamation and vacuolisation of tubular epithelial cells in kidney, were observed. Quantification of lindane in water and whole fish samples was performed using a gas chromatograph equipped with an electron capture detector. The results of this histological analysis of various fish tissues indicate a direct correlation between pesticide exposure and the histopathological disorders observed. Chemical analysis of the lindane in the water and fish tissues confirmed a causal relationship between exposure to this pesticide and the fish damage found.