Sequential corrected creatinine clearance (CCC) evaluations were obtained in 30 patients treated with intra-arterial and/or intravenous cis-diamminedichloroplatinum-II (CDP). The dose was 150 mg/M2 administered with mannitol diuresis at 2 to 3 weekly intervals. Four hundred fifty-three courses were administered (range, 6-18) over 18 months. Patients also were treated with 283 courses of high-dose methotrexate (MTX) and citrovorum factor "rescue" which were interposed between treatments. Deleterious effects of cumulative courses of CDP manifested as progressive reductions in CCC and delayed excretion of serum MTX. Severe MTX toxicity was aborted by augmenting the fluid intake and prolonging citrovorum factor rescue when elevated levels of serum MTX were detected. The first indication of renal induced CDP toxicity occurred with a cumulative dose of 450 mg/M2. At the termination of treatment (cumulative CDP dose over 1050 mg/M2) renal impairment still was present.