Renal dysfunction is a well-known dose-limiting toxicity of cis-platinum. Previous studies demonstrated a 32% incidence of nephrotoxicity following a 100 mg/M2 single dose of cis-platinum with mannitol diuresis. WR-2721 is an aminothiol which in the animal model improves renal tolerance to cis-platinum by factors of 1.3 to 1.7. Phase I trials were initiated to establish the toxicity when WR-2721 was given prior to escalating doses of cis-platinum. Fifty-two patients received 161 courses of WR-2721 prior to cis-platinum (60-150 mg/M2) with mannitol and hydration. Nephrotoxicity, measured by twice weekly serum creatinines and monthly creatinine clearances, occurred in only 10/97 (10%) courses with 120 mg/M2 of cis-platinum. No patient experienced a creatinine elevation after 135 mg/M2 of cis-platinum. With 150 mg/M2 of cis-platinum, 6/17 (35%) courses were associated with transient nephrotoxicity. Five patients who developed transient creatinine elevations following 150 gm/M2 of cis-platinum were subsequently retreated with WR-2721 and cis-platinum (100 mg/M2) without nephrotoxicity. Bone marrow suppression was mild and infrequent. Mild to moderate peripheral neuropathies were noted in seven patients following cumulative cis-platinum doses ranging from 460-1160 mg/M2. Objective partial responses were observed in 26/45 (58%) patients with measurable or evaluable disease. Thus, there is no evidence that WR-2721 protects against the antitumor efficacy of cis-platinum in man. Compared to retrospective series, our data suggest that WR-2721 may provide some protection against platinum-induced nephrotoxicity and neurotoxicity. Controlled trials will be required to define the potential clinical benefit of WR-2721 and cis-platinum.