We examined the ability of twenty-five hearing-impaired and eight normal-hearing listeners to discriminate between release time constants used for compression in hearing aids. The compressor was a standard three-channel system. The stimuli were normal and 'vocoded' sentences from a male and female database. In agreement with other studies looking at different outcomes, performance varied greatly across individuals. This variation was greater in hearing-impaired listeners, for whom the discriminability of a release time of 5 ms from one of 5000 ms (with the attack time fixed at 5 ms) ranged from chance to perfect. This variability was not significantly related to hearing impairment nor to individuals' compression ratios.