Morphophonological alternations in English words such as able versus ability involve changes in both stress and vowel quality. This study examined how native speakers of Spanish and English produced four such morphologically related English word pairs. Degree of stress and vowel quality was assessed auditorily and instrumentally. Stress placement generally seemed to constitute less of a learning problem for the native Spanish speakers than vowel reduction. The results suggest that Englishlike stress placement is acquired earlier than vowel reduction and that the ability to unstress vowels is a necessary, but not sufficient, condition for vowel reduction. The magnitude of stress and vowel quality differences for the four word pairs suggests that L2 learners acquire stress placement and vowel reduction in English on a word-by-word basis. © 1989, Cambridge University Press. All rights reserved.