A recently described collagen gel culture technique has been modified to evaluate the growth characteristics and chemosensitivity patterns of genitourinary neoplasms. Fresh human surgical explants incorporated radiolabeled DNA precursors [H3)thymidine or deoxyuridine) in 97% of 38 patient specimens (18/19 bladder, 3/3 prostate, 2/2 testis, 13/14 renal), after being maintained for three to 13 weeks/passage, with several specimens reaching their sixth passage (20 months). Control cellular DNA incorporation ranged from five to 90% (#cells labeled/#cells evaluated), with median labeling for bladder 30%, prostate 80%, testis 90%, and renal 80%. Original histopathologic classification was maintained in all cases. Tumor volume and glucose consumption were other measurable parameters. Seventy-three surgical specimen cultures were treated with chemotherapeutic agents after a minimum of four weeks in culture. Single agent exposures were 24 hours at 1X and 10X reported peak plasma concentrations. Combination agents were sequenced as in current clinical protocol for bladder tumors and fourteen day continuous fluorodeoxyuridine (FdURD) exposure for renal tumors. Sensitivity was found in 1/2 prostate and 1/10 renal tumors to Adriamycin, 8/15 bladder and 1/2 testis tumors to cisplatin, 11/28 renal tumors to FdURD and 6/16 bladder tumors to MVAC combination chemotherapy. This culture system offers the advantages of in vivo-like solid tumor growth, a high culture success rate, longevity in culture, maintenance of the primary histopathology and reproducible chemosensitivity response.