Surgical tumor specimens obtained from twenty-five patients with renal cell carcinoma were subjected to the gel-supported culture developed by Hoffman for a clinical approach. Cell viability was determined by exposure to 3H-thymidine. The anti-cancer drugs examined in this set were 13 in total: ADM, AMR, BLM, MMC, VCR, VLB, etoposide, CDDP, 5-FU, MTX, IFN-alpha, IFN-gamma and TNF. The specimens were exposed to media containing 1x and 1/10x achievable human plasma peak concentrations of the agents. The overall susceptibility rate for growing tumors obtained from patients was 88% (22 of 25 patients). Susceptibility (less than 50% of control 3H-thymidine uptake) to ADM was observed to be highest (56%) in 12 of 22 patients, and to VLB and BLM (50%) in 11 patients each. On the other hand, that to MTX was observed in 1 patient at the lowest rate (5%), and that to the BRM group drugs was observed in 3 in IFN-alpha (14%), 1 in IFN-gamma (5%) and 2 in TNF (9%). However the number of effective drugs was not correlated to the grade, architecture and cell type. These results suggest that this assay system may be useful for a chemosensitivity test.