Albino and pigmented guinea pigs were exposed to 20 kHz at 120 dB SPL for exposure durations of 30, 7.5, 6.5, 5 and 3.25 min. In a second series of experiments, the two shortest exposures were repeated after an interval of 6 or 24 h. Sensory hair cell loss was assessed 3 weeks post-exposure by surface preparations and quantified as percentage cell loss per segment per row, total numbers of outer and inner hair cells lost and the area of total outer hair cell damage. A variable but discrete area of damage resulted from these exposures. The main differences between the two strains were that in albino guinea pigs fewer ears were damaged after the shortest single exposures and generally more damage occurred after repeated exposures. However, no differences were detected in either strain when the interval between repeated exposures was changed.