The relative benefits of binaural as opposed to monaural hearing aids were assessed by the use of a diotically presented, audiovisual speech-in-noise task in a group of bilateral, severely hearing-impaired individuals. Significantly greater benefit was gained from binaural amplification, irrespective of hearing level and degree of asymmetry. The benefit was considered to be due to central summation. It is concluded that binaural amplification should be attempted in all bilateral, severely hearing-impaired subjects. About 80% will accept this and be able to demonstrate benefit in an audiovisual task.