We retrospectively evaluated the usefulness of an in vitro human tumor culture system using a specialized collagen gel matrix derived from pig skin as a chemosensitivity test for human gastric carcinomas, especially for scirrhous gastric carcinomas. Seven xenograft tumors derived from human gastric cancers were examined by using this system and the results were compared with the data obtained from a nude mouse assay. Xenograft tumors exhibited three-dimensional growth on the collagen gel matrix like that in vivo. The drug sensitivity as measured by this assay at 10 times therapeutic peak plasma concentrations of the drugs corresponded with that measured by the nude mouse assay for all xenograft tumors. The correlation coefficients were 0.873 for cisplatin, 0.919 for etoposide, 0.880 for mitomycin C and 0.932 for adriamycin. In the case of scirrhous gastric carcinoma, the drug sensitivity could be measured successfully in all 12 patients. This in vitro assay system has advantages as a chemosensitivity test because of its convenience, rapidity, and in vivo-like three-dimensional tumor growth. This system should contribute to the development of chemotherapy for scirrhous gastric carcinomas.