To determine the auditory toxicity effects of long-term cis-dichlorodiammineplatinum II therapy, pure tone hearing thresholds were measured prior to therapy and repeated before each subsequent treatment. CDDP was given by a slow intravenous drip method at a low dose of 1 mg/kg body weight, with 37.5 gm mannitol, once a week for six treatments and every 3 weeks thereafter. From a group of 173 genitourinary cancer patients treated, 50 male patients were selected who received at least 12 months of CDDP with no active conductive ear pathology, and whose audiograms obtained at baseline, 6th weeks, 26th weeks, and 52nd weeks of treatment were all available for comparison. Pure tone threshold levels deteriorated across time particularly by the 52nd week and at the higher frequencies. Threshold differences across time were statistically significant and within a linear trend. Of the 50 cases, 30% showed suspect or no ototoxicity, 26% mild, 32% moderate, 2% marked, and 4% showed severe ototoxic changes. Of the two cases who developed severe ototoxicity, one showed complete recovery. There was partial recovery in 26% and no recovery in 54%. Individual variability in susceptibility to and recovery from ototoxicity necessitates systematic audiometric monitoring throughout the therapy.