For prevention and therapy of peritoneal dissemination, a new dosage from (MMC-CH) comprising carbon particles adsorbing mitomycin C was given to 44 patients (the MMC-CH group) undergoing gastrectomy for gastric cancer, of which advancing stage was classified into the category of H0, and S2 or S3, and P0, P1, P2 or P3 according to the General Rules for the Gastric Cancer Study. MMC-CH, principally at 50 mg person in terms of mitomycin C was administered intraperitoneally before the surgical wound was closed. Historical control group was composed of 53 patients not given MMC-CH, who underwent gastrectomy for gastric cancer in the same advancing stage as those of the 44 patients. There was statistically no significant difference of age, sex, depth of infiltration, macroscopically and microscopically defined progression of lymph-nodal metastases, between the MMC-CH group and the historical control group. The survival rate of the overall patients, and each group of the patients with the lesion defined as P0, P1, P2, or P3 was compared with Kaplan-Meier's method between the MMC-CH group and the historical control group. In the MMC-CH group, the survival rates of the overall patients and the patients with P0, P1, or P2 lesion were statistically significantly higher than those in the historical control group. However, the rate of the P3 patients in the MMC-CH group was statistically significantly lower than in the historical control group.