Preclinical evidence has suggested that disulfiram (DS) and related compounds can decrease the toxicity and enhance the therapeutic index of cisplatin (CP). To study this further, we have performed a prospective randomized study wherein 53 patients with CP-sensitive malignancies were assigned to therapy with CP 100 mg/m2 alone (group I) or CP 100 mg/m2 and oral DS 2,000 mg/m2 (group II). Both groups were comparable with regard to sex distribution, age, performance status, prior chemotherapy, and radiotherapy. Twenty-three patients were not evaluable for response (3 refused follow-up, 18 had less than two courses, one had an early death, and one had excessive toxicity during the first cycle of treatment). Of the 30 evaluable patients (16 in group I, 14 in group II), only one in group II achieved a complete response. There was no statistically significant difference in response rate, time to progression, or median survival between the two groups. Fifty-two patients (98.1%) were evaluable for toxicity. Significant differences in toxicities were observed between the two groups: patients in group I encountered lower [Eastern Cooperative Oncology Group (ECOG) 0-1)] grades of nausea, vomiting, and ototoxicity, and patients in group II experienced higher grades (ECOG 2-3) of toxicity in general. In addition, there was no difference in nephrotoxicity between the two groups, as measured by the change in serum creatine or 24-h urine creatinine clearance over the first course of treatment. We conclude that, contrary to previously published reports, DS does not afford significant nephroprotection against CP and, in fact, enhances gastrointestinal and ototoxicities.