Histopathological alterations induced by Thiodan (R) in three tissues, namely, digestive gland, foot and mantle, of the freshwater snail Lymnaea stagnalis were investigated. Specimens of Lymnaea stagnalis were exposed to 0.36% and 0.72% Thiodan (R) 35 EC, a commercial grade of endosulfan, for 96 h followed by a recovery period of 30 days. Thiodan (R) caused significant dose dependent histopathological changes in all the tissues of the snail. Irreversible necrotic changes occurred in the digestive gland of the snail following Thiodan (R) exposure. Degenerative changes in the muscle fiber of the foot, protein and pigment cells of the foot and the connective tissue element of the mantle were recovered after 30 days of recovery of the snail in pesticide-free freshwater. Copyright (c) 2005 John Wiley & Sons, Ltd.