Renal function in 24 patients with disseminated nonseminomatous testicular carcinoma treated with combination chemotherapy including cis-platinum was examined prospectively. Renal function was monitored by several determinations of glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and serum creatinine, and beta-2-microglobulin. A reduction in GFR and ERPF was found at the end of the induction chemotherapy and at six weeks thereafter. Median GFR and ERPF decreased both 23% (P less than 0.01). Serum creatinine and beta-2-microglobulin concentrations however did not rise. It is suggested that under the influence of chemotherapy with platinum the production of creatinine and beta-2-microglobulin is decreased rendering their serum levels unsuitable as parameters of renal function.