The protective effect of a whey protein concentrate (WPC) was studied in three models of stomach ulcerative lesions induction: subcutaneous injection of indomethacin, and stress induced by either intraperitoneal injection of reserpine, or immobilization and holding in the cold (4 degrees C, 2 hours). Adult Wistar rats (300-400 g) were used for acute (single-dose), repetitive, or subchronic (10 days) administration of WPC prior to treatment with the ulcerogenic factors. The best protection was achieved in the indomethacin model for repetitive and subchronic experiments, reaching 50.1% and 44%, respectively, inhibition of the ulcerative lesions, which was significant at 1% probability (P <.01). For the immobilization and cold model, maximum inhibition by WPC was 22.1%, and that for the reserpine model was 23.8%. In both models the inhibition was not significant (P >.05) compared with saline (negative control).