In 40 CAPD patients treated for peritonitis, the authors did a prospective study of ototoxic effects of intraperitoneal tobramycin. They evaluated cochlear function in pure-tone threshold audiograms over a range of frequencies from 250-10,000 Hz, in the speech-reception threshold test and in the speech-discrimination test. These tests were performed within 48 hours of initiation of tobramycin treatment and within 2 or 3 weeks of the drug's discontinuation. With the aminoglycoside doses used in this study, no statistical difference between the mean baseline and mean follow-up hearing levels was seen in these 40 patients. However, according to the standard criteria of ototoxicity, the hearing in 10 of 40 patients (25%) deteriorated after tobramycin, while it improved in seven patients (17.5%). In the remaining 23 (57.5%), hearing remained stable. With respect to the risk factors for ototoxicity such as advanced age, increased duration of treatment, elevated plasma aminoglycoside levels, concomitant treatment with other ototoxic drugs, pre-existing hearing loss, renal dysfunction and hyperthermia, no statistically significant difference was demonstrated between the patients with deteriorated, stable or improved hearing. The results of this study do not confirm that tobramycin given intraperitoneally to CAPD patients produces auditory toxicity. The hearing deterioration observed in 10 patients may be due to synergistic factors. The improvement observed in 7 patients could not be explained.