The urinary excretion of leucine aminopeptidase (LAP), N-acetyl-beta-glucosaminidase (NAG), and beta 2-microglobulin was measured in 12 cancer patients receiving cis-platinum to evaluate the sensitivity of these indices for renal tubular damage. NAG and LAP excretion rose markedly in all patients, and beta 2-microglobulin rose in 11. Seven of the 9 patients who had received cis-platinum 6 wk before the study had prestudy dose elevations of one or more of these indices. We conclude that these urinary proteins are sensitive indicators of proximal renal tubular injury and may provide greater sensitivity for comparison of the nephrotoxic potential of future platinum analogs or for assessing the efficacy of regimens designed to protect the kidney from platinum nephrotoxicity than other measurements. The persistence of high excretion vales for these indices 6 wk after a dose demonstrates the persistent renal injury by cis-platinum.