English monolinguals and native Spanish speakers of English used a 9-point scale to rate syllable-initial stops for goodness as realizations of the English /p/ category. Voice onset time (VOT) was varied in a set of short-duration (‘fast-rate’) consonant-vowel (CV) stimuli, and in a set of longer-duration (‘slow-rate’) CV stimuli. The VOT values ranged from values typical for English /b/ to values which exceeded those typical for English /p/. Results for the native English (NE) subjects replicated those obtained previously using the same two continua. Goodness ratings systematically increased, then decreased as VOT values extended beyond the range typical for English /p/. The NE subjects gave their highest ratings to stimuli with VOT values of about 50 ms. For stops with longer VOT values, their ratings were higher for stimuli in the slow-rate than fast-rate continuum. The native Spanish (NS) subjects were assigned to two subgroups based on degree of foreign accent in their pronunciation of English sentences. Both proficient and nonproficient NS subjects gave their highest ratings to stimuli with much the same VOT values as the NE subjects, even though /p/ is realized with short-lag VOT in Spanish. The nonproficient, but not the proficient NS subjects showed significantly smaller rate effects on goodness ratings than did the NE subjects. However, the subjects in both NS groups gave significantly higher ratings to stimuli with short-lag VOT values than did the NE subjects. The results are discussed in terms of the hypothesis that adult learners of a second language may establish new perceptual phonetic categories for phonetic segments not found in the native language. © 1995 S. Karger AG, Basel.