In a study on the effects of a frequency-dependent automatic gain control in hearing-aids, two experiments were carried out with hearing-impaired listeners. In the first experiment, the effect of varying the amplitude-frequency response on the speech-reception threshold (SRT) of sentences presented in noise was studied. The noise had the same spectrum as the long-term average spectrum of the sentences. Results suggest that the amplitude-frequency response may vary within a range from, roughly, -3 to +10 dB/oct relative to the bisector of the dynamic range, without giving an increase in SRT larger than 2 dB. In the second experiment, the effect on masked SRT of adjusting the amplitude-frequency response to situations of seriously interfering low-frequency noise was studied. Again, the noise had a spectrum identical with the long-term average spectrum of the sentences, but this time the noise level in one octave band was increased by 20 dB. Preliminary results indicate that a selective attenuation of the signal in the band containing the extra noise may give a decrease of masked SRT up to 4.5 dB.