For assessment of the ototoxic potential of carboplatin [cis-diammine-1,1-cyclobutane dicarboxylate platinum(II); CBDCA], pure-tone audiograms were evaluated in 27 patients receiving a total of 119 doses of carboplatin in the range of 300-400 mg/m2. Pure-tone audiometry (PTA) was done immediately prior to and 4 weeks after the administration of 80 doses (67%). Defining carboplatin ototoxicity as an increase of greater than or equal to 30 dB in auditory thresholds that was unexplainable by other causes, we identified 5 examples (19%). Hearing loss tended to be cumulative with increasing dose and was always maximal at 8,000 Hz. Two patients had an increase in auditory thresholds at 1,000 Hz, but this only amounted to 10 dB in each case. Patients developing ototoxicity tended to be older. Sex, the pre-treatment creatinine clearance, the pretreatment audiogram, the number of doses, and the cumulative dose did not emerge as being reliable predictors of subsequent ototoxicity. We conclude that although carboplatin is ototoxic, clinically significant deafness does not occur with conventional dosing and routine audiometric monitoring is therefore unnecessary. However, we suggest that caution should be exercised when carboplatin is given either at higher doses or for longer periods when there is concomitant use of other potentially ototoxic agents or when there is significant pre-existing auditory impairment.