Ototoxicity affects the higher frequencies first and extends to the lower frequencies during continuation of the ototoxic treatment. Peritonitis due to continuous ambulatory peritoneal dialysis (CAPD) regularly demands ototoxic antibiotic treatment, e.g. with gentamicin and vancomycin. In this study ultra-high frequency audiometry (10-20 kHz), 'normal' audiometry (0.125-8 kHz) and registration of blood concentrations of the antibiotics were used to assess ototoxic hearing loss during treatment of CAPD patients with peritonitis.