The authors had previously reported that the accumulation of p53 is clearly demonstrable in microwave-fixed, paraffin-embedded sections of colorectal carcinomas. In the present paper, the authors performed an immunohistochemical study of p53 in gastric carcinomas prepared by microwave irradiation. Using a monoclonal antibody (PAb1801), nuclear p53 was detected in 22 of 45 (49%) cases of gastric carcinoma, and no staining for p53 was demonstrated in the adjacent normal epithelium, including areas of intestinal metaplasia. The incidence of p53 accumulation was not affected by clinical features, such as tumor stage, depth of invasion, and metastasis; however, positivity for p53 was significantly higher in intestinal-type carcinomas (56%) than in diffuse-type (27%) carcinomas. Furthermore, a large number of carcinoma cells expressed p53 in the intestinal-type, but only a few cells were positive for p53 in the diffuse-type. The results of the present immunohistochemical study of p53 accumulation in gastric carcinomas suggest that gene alterations of p53 are not rare in gastric carcinomas and may participate in the carcinogenesis of intestinal-type carcinomas of the stomach.