We assessed the acute and chronic effect of multiple courses of cisplatin therapy on renal tubules by monitoring the urinary excretion of alanine aminopeptidase, N-acetyl-beta-D-glucosaminidase, and total protein. Urine specimens were obtained before and after doses of cisplatin (90 mg/m2) given to 12 patients. Each dose of cisplatin induced transient increases in enzyme excretion, followed by proteinuria 3-5 days later. Transient enzymuria after the last cisplatin dose was significantly greater than that after the first dose. Moreover, persistent increases in urinary N-acetyl-beta-D-glucosaminidase and serum creatinine concentrations over pretherapy levels indicated chronic renal tubular damage. Our findings disclosed striking differences between patients in susceptibility to progressive nephrotoxicity.