The effects of varying levels of dietary vitamin C on the incidence of aspirin-induced gastric hemorrhagic lesions were studied in young, male rats. Rats fed diets containing either 20, 40, or 60 mg of L-ascorbic acid per gram of diet did not exhibit focal gastric lesions. Administering a single oral dose of aspirin (30 mg aspirin/100 g of body weight) to rats fed control diets produced gastric lesions. When the rats were given aspirin plus a diet containing either 40 or 60 mg ascorbic acid per gram of diet, there was a significant increase in number of gastric lesions. Since vitamin C and aspirin seem to act synergistically in producing hemorrhagic lesions in the stomach, it is recommended that all individuals taking megadoses of vitamin C be cautioned against taking aspirin concurrently.