Subrenal capsule assay as a chemosensitivity test for primary esophageal squamous cell carcinoma. The efficiency of the subrenal capsule assay (SRCA) was studied with fresh tissue of esophageal squamous cell carcinoma. The day-to-day changes in 10 carcinoma cases were evaluated for 9 days. The cancer cells continued to proliferate from the 3rd to the 7th day after the implantation and then decreased. The host reaction was recognized histologically from the 3rd or 4th day to the 9th day. However, the immune reaction did not significantly influence the evaluation of SRCA until the 7th day. The immunohistochemical staining with anti-bromodeoxyuridine monoclonal antibody revealed the existence of cancer cells at the DNA synthesizing stage (S stage) in the graft until the 7th day. In chemosensitivity test by SRCA, 21 patients were studied, and all were evaluable. 5-FU administration produced a response in 8/21 cases (38.1%), VDS in 8/21 (38.1%), and CDDP in 3/21 (14.3%). Used in combination, CDDP + VDS was effective in 7/18 cases (38.9%) and CDDP + BLM in 6/18 cases (33.3%). 