The effects of a single dose of cis-diamminedichloroplatinum (DDP) on the kidney function were investigated in 14 patients with disseminated malignancy and normal renal function. A single dose of DDP (30-50 mg/m2) caused severe proximal tubular dysfunction with increased urinary losses of calcium, magnesium, and amino acids. Phosphate excretion was not affected. DDP can cause proximal tubular dysfunction and close attention must be paid to serum calcium and magnesium levels.