Two experiments used object-manipulation tasks to examine whether one- to two-year-olds form superordinate-like categories by attending to object parts. Findings indicated that 14- and 18-month-olds behaved systematically toward categories with different, but not matching, parts. Without part differences, none formed superordinate categories. Younger infants categorized by parts rather than by category membership, suggesting a perceptual basis for categorization. (Author/KB)