Previous studies have indicated that sodium diethyldithiocarbamate (DDTC) can reduce cisplatin's (CP) toxic effects without altering the antitumor activity. DDTC has also been shown to have immunostimulative properties. Sixty patients with objectively measurable recurrent and/or metastatic squamous cell carcinoma (SCC) of the head and neck were randomized to receive either (A) CP at 120 mg/m2 over one hour on day 1, plus fluorouracil (5-FU) at 1,000 mg/m2 over 24 hours as a continuous infusion on days 1 through 5, or (B) CP/5-FU as in A, plus DDTC at 600 mg/m2 over 30 minutes administered intravenously (IV) exactly 30 minutes after CP infusion. Group B also received DDTC at 200 mg/m2 administered IV over 30 minutes on days 8 and 15. Each cycle was repeated at 3-week intervals. Objective responses were achieved in 41% of the CP/5-FU group and in 29% of the CP/5-FU with DDTC group (P = .26). Median survival was 9 months in group A and 10 months in group B. CP-related toxicity between the groups was equivalent with respect to nausea and vomiting, renal impairment, neurotoxicity, ototoxicity, and hematologic toxicity. The pharmacokinetics of reactive platinum species in plasma ultrafiltrate and urine samples obtained from both groups were comparable. The immune status of 48 patients was evaluated before and after completion of therapy. There were no significant differences in mean pretreatment and posttreatment values within or between groups A or B, except for absolute pretreatment OKT4 values (P = .02). We conclude that (1) the present dose and infusion schedule of DDTC did not significantly reduce CP-mediated toxic effects, (2) DDTC did not alter the disposition of ultrafilterable platinum species, (3) DDTC did not affect immune responses, and (4) the addition of DDTC improved neither the clinical response nor the survival of patients with recurrent SCC of the head and neck.