Vowel identification was tested in quiet, noise and reverberation with 20 normal-hearing subjects and 20 hearing-impaired subjects. Stimuli were 15 English vowels spoken in a /b-t/ context by six male talkers. Each talker produced five tokens of each vowel. For hearing-impaired subjects, some vowels were confusable even in undegraded listening conditions and for normal-hearing subjects some vowels became confusable in degraded listening conditions. Apparently, both degradation of listening conditions and perceptual limitations introduced by hearing impairment caused reduction of available information in the vowels. Examination of error clusters allowed an indication of which segments of the vowels were masked by noise or by reverberation and which segments were not perceived by hearing-impaired subjects. Spectral analysis of the vowel stimuli revealed differences in detailed structure among vowels produced by various talkers and among the five tokens produced by each talker. As a result of these differences, error clusters were dependent upon talker and upon particular vowel token.