Forty rats were housed in standard activity wheel cages and fed for only 1 hr per day. The animals were equally divided into 4 groups that received either saline, 12.5 mg/kg, 25.0 mg/kg or 50.0 mg/kg of metiamide, an H2 receptor antagonist, 3 times a day. All animals died within 11 days and all demonstrated significant gastric lesions in the glandular fundus of the stomach. The 50.0 mg/kg dosage group, however, demonstrated significantly fewer ulcers than the saline animals and the lesions that did occur were significantly smaller than those noted in the control animals. Several hypotheses were offered to explain these results which took into account metiamide's effects on gastric secretion and motor activity. It was suggested that secretion of acid may be an important contributing factor in the formation of gastric ulcers in animals subjected to the "activity-stress" procedure.