Anyone who has struggled to communicate in a noisy cafeteria will probably agree that, at some point, reverberation seems to cause problems, but for architects to design better rooms we need to know how much is tolerable and what aspects of room design influence the need for acoustic damping. The distorting effect of reverberation on speech is being extensively explored, but reverberation also has a detrimental effect on listeners' perceptual segregation of speech from interfering sounds, such as competing speech. The latter effect has been less well explored and may be much more significant in spaces designed for social interaction. In anechoic conditions, the auditory system can exploit differences in the fundamental frequency and the spatial location of competing voices in order to extract a target voice from an interfering one. Evidence to date indicates that moderate reverberation can greatly impair these abilities, but also that simple measures of reverberation time are poor predictors of this impairment. These data will be presented and explained, and our approach to developing more appropriate predictive statistics will be introduced.