The effect of cis-diamminedichloroplatinum (DDP) on plasma and urinary zinc was studied in fifteen patients with squamous cell carcinoma. A decrease in plasma zinc accompanied by an increase in urinary zinc excretion was observed. Pretreatment plasma or urinary zinc did not correlate with tumor size or site, nor was there a correlation between changes in these measurements and a response to therapy. The enhanced excretion of urinary zinc may be related to a decrease in amino acid resorption in the proximal tubule. It is concluded that DDP administration may result in hyperzincuria and could potentially precipitate a symptomatic zinc deficiency state.