The aim of this study was to assess the effect of speaking rate changes on the perception of English stop consonants by four groups of subjects: English and Spanish monolinguals, ’early’ Spanish/English bilinguals who learned English in childhood, and ’lat’ bilinguals who learned English in adulthood. Subjects identified, and then later rated for goodness as exemplars of the English /p/ category, the members of two voice onset time (VOT) continua. The English monolinguals identified a well-defined range of VOT stimuli as English /p/, and stimuli with longer VOT values as ’exaggerated’ instances of English /p/. Their goodness ratings increased as VOT increased, then showed a systematic decrease as VOT began to exceed values typical for English /p/. The English monolinguals’ goodness ratings also varied systematically as a function of speaking rate, which was simulated in the two continua by varying syllable duration. The Spanish monolinguals, on the other hand, failed to consistently identify any of the stimuli as English /p/. Although speaking rate influenced their goodness ratings, the Spanish monolinguals’ rate effects differed significantly from the English monolinguals’. The early bilinguals resembled the English monolinguals, and differed from the Spanish monolinguals to a greater extent than did the late Spanish/English bilinguals. This was taken as support for the hypothesis that early bilinguals are more likely than are late bilinguals to establish new phonetic categories for stop consonants in a second language. © 1996 S. Karger AG, Basel.