Histopathological alterations in three tissues, namely, digestive gland, foot and mantle of the freshwater snail Galba truncatula induced by Thiodan (R) 35 EC, a commercial preparation of endosulfan, were studied in the laboratory. The snails were exposed to five sublethal concentrations of Thiodan (R), two of them higher concentrations at 0.33% and 0.65% in glass jars for short-term exposure (96 h) and three of them lower concentrations at 0.08%, 0.16% and 0.27% for long-term exposure (10, 20 and 30 days). Thiodan (R) caused significant histopathological changes in the tissues of the snail, irrespective of the concentration of the pesticide and its exposure period. The histopathological changes included accumulation of amoebocytes in the hemolymphatic spaces between the tubules of the digestive gland, exudation in the lumen of tubules, expansion of hemolymphatic spaces between the tubules and increase of vacuolation and necrotic changes in the digestive cells. Disruption of columnar muscle fibers and alteration of epithelial layers were detected in the foot and mantle of the treated specimens. The number and size of mucous and protein cells in the foot and mantle also changed. Copyright (c) 2005 John Wiley & Sons, Ltd.