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 experiments. These results are not compatible with a strict interpretation of the categorical perception of stop consonants.