Looking times of 36 children were recorded during subject-controlled presentation of slides in order to determine whether the existence of simple categories in 3-year-olds can be inferred from habituation data, and to determine any sex differences in conceptual generalization of habituation. Habituation was demonstrated over repeated presentation of 6 slides from a single conceptual category (e.g., animals). In an immediate generalization test the six habituated slides were intermixed with 6 unfamiliar, but similar, slides from the same category and 6 slides from a novel category (e.g., fruits). Mean looking times were shortest for familiar slides, longer for categorically similar slides, and longest for categorically novel slides. Females showed generalized habituation from the familiar slides to the categorically similar slides, but looked significantly longer at those from the novel category. Males looked significantly longer at new slides from either the similar or the novel category than at the familiar slides, but on unfamiliar slides did not significantly discriminate between the similar and novel categories. (Author/SB)