The in vitro drug sensitivity of gastric cancer tissues obtained from 40 patients with advanced cancer was compared in terms of the pathological classifications which were assigned according to the General Rules for the Gastric Cancer Study in Surgery and Pathology in Japan. Cases of poorly differentiated adenocarcinoma which had penetrated the serosa were evaluated using the succinate dehydrogenase inhibition (SDI) test for determining the in vitro chemosensitivity. The sensitivity of the stage III group to cisplatin was higher than that of the stage IV group. Although there were no statistical differences in drug sensitivities according to macroscopic findings (Borrmann's classification), the expanding growth type was more susceptible that the infiltrating type to cisplatin, aclacinomycin A (ACR) and carboquone (CQ) microscopically. In cases of lymph node metastasis [n(+)] the sensitivity to cisplatin, ACR, CQ, adriamycin and mitomycin C was less than in those with or without primary lymph node metastasis [n(-)]; lymphatic invasion in the gastric wall (ly) was a significant factor linked to drug resistance. Our findings indicate that the evaluation of tumor pathology is important in predicting the chemosensitivity of poorly differentiated gastric cancers.