Four experiments, all of which focused on vowel duration, assessed Chinese subjects' production and perception of the contrast between/t/ and/d/ in the final position of English words. Vowel duration was measured in minimal pairs in the first experiment. the stimuli in natural-edited beat-bead and bat-bad continua in which vowel duration varied in 20-ms steps were then presented to native English and Chinese subjects in a forced-choice test, in an experiment using the method of adjustment, and in an imitation task. the non-natives who learned English in childhood closely resembled native speakers in all four experiments. Three groups of non-natives who had learned English as a second language in adulthood, on the other hand, differed from the native speakers. The late learners produced significantly longer vowels in words ending in/d/ than/t/. However, the late learners' vowel duration differences were much smaller than the native speakers', and were correlated significantly with degree of foreign accent in English. The late learners differed from the native speakers in several ways in the two perception experiments, and also in the imitation task. The pattern of significant and nonsignificant between-group differences, but not data for individual subjects, was consistent with the hypothesis that L2 (second language) production accuracy is limited by the adequacy of perceptual representations for sounds in the L2. © 1993, Acoustical Society of America. All rights reserved.