Three experiments directly compared infants' categorization in variations of the visual familiarization task. In each experiment, 4- or 6-month-old infants were familiarized with a collection of dogs or cats and then their response to novel dogs and cats was assessed. In Experiment 1, 4-month-old infants responded to the exclusive distinction of dogs or cats when tested in a paired-comparison task. In Experiments 2 and 3, 6-month-old infants, but not 4-month-old infants, responded to this same distinction in a successive presentation task, even when the amount of familiarization was equated to that of the paired comparison task. Therefore, familiarization with a particular set of stimuli does not induce infants to respond to a single category but rather they respond to different categories depending on features of the task. (Contains 1 table and 3 figures.)