The discriminability of bilabial stop consonants differing in VOT (the Abramson-Lisker bilabial series) was measured in a same—different task, an oddity task, and a dual response, discrimination-identification task. Subjects showed excellent within-category discrimination in all three tasks after a moderate amount of training in a same—different task with a fixed standard and with feedback. In addition, discrimination performance continuously improved with increasing stimulus difference for both intra and intercategory comparisons. Also, subjects were able to alter their identification responses so that well-defined category boundaries fell at arbitrary values determined by the experimenters. These results are not compatible with a strict interpretation of the categorical perception of stop consonants.