Clinicopathological study was undertaken on gastric carcinoma, 130 cases and 145 lesions, treated with preoperative anticancer chemotherapy, using Oboshi-Shimosato's criteria for histologic grading of effects. The results were as follows: Not only morphologic manifestations observed by X-ray and endoscopy, but also histopathologic findings of biopsied specimens taken after treatment with 5-FU for 12 consecutive days, were effectively used for judging the sensitivity of cancerous tissue to anticancer agents in vivo. Effective rates were high in cases treated with oral administration of 5-FU more than 500 mg/day and 5.0 gr as a total dose (p less than 0.01), and the incidence of anticancer-induced-gastritis was also seen high in cases with oral administration of 5-FU more than 500 mg/day and 6.0 gr as a total dose (p less than 0.005). The proper dosage of 5-FU orally administered was, therefore, 500 mg/day and 5.0 gr. as a total dose. Histologic effects of anticancer agents on primary lesions were in accordance with those of metastatic foci of lymph nodes (p less than 0.01). 5-FU when orally administered resulted in a low rate of significant toxicity (23.5%), and no serious side-effects. In conclusion, it is considered that preoperative anticancer chemotherapy on gastric carcinoma apparently causes cancer cell death, decrease viability of cancer cells, makes it possible to detect in-vivo sensitivity for anticancer agents, and will improve the late survivals of patients with gastric carcinoma.