A commercially available programmable BTE hearing aid with 3-channel AGC (Siemens, Triton 3000) was compared to the subjects' own single-channel compression aids in a group of experienced hearing aid wearers. Two cross-over frequencies, three AGC onset levels, and three channel amplifications were programmable. The maximum output level was controlled by conventional peak clipping. The frequency response of the multichannel system was matched to the individuals' own aids which had been fitted in the two years prior to this study. Frequency response shaping was accomplished by real ear measurement monitoring. The performance of the hearing instruments was measured by (1) speech audiometry in noise and (2) subjective judgement of sound quality and speech intelligibility. Speech recognition was tested using rhyme test material in noise in a group of 10 subjects with sloping high-frequency hearing loss as well as in a group of 16 individuals with nearly flat audiograms. In both subgroups speech recognition scores (S/N: -5 to 15 dB) were 7 to 20% higher for the 3-channel AGC device compared to the single-channel AGC instruments. This finding is equivalent to an improvement of the S/N ratio of about 7 dB for the user. The results of the subjective judgements were similar for both subgroups. Sound quality and speech intelligibility were mostly rated as "very good" or "good" on a 5-point-scale. The subjects were also asked to compare the performance of their own hearing aids with the 3-channel AGC instrument; the latter generally turned out to be preferable.(ABSTRACT TRUNCATED AT 250 WORDS)