The signal-to-noise ratio necessary for a constant performance level was determined for normally hearing and hearing-impaired subjects under three levels of reverberation (0.3, 0.6, and 1.2 s) with monaural and binaural hearing aids having directional and omnidirectional microphones. Results indicated (a) a significant binaural advantage (2-3 dB) which was independent of microphone type and reverberation time, (b) a significant directional microphone advantage (3-4 dB) which was independent of hearing aid arrangement (monaural or binaural) but dependent on level of reverberation, (c) a significant reverberation effect which was larger than either the binaural or directional microphone effect, and (d) additive binaural and directional microphone advantages. The results suggest that the signal-to-noise ratio is optimized when binaural hearing aids with directional microphones are used in rooms with short reverberation times.