Infants watched an experimenter retrieve a stuffed animal from an opaque box and then return it. This happened twice, consistent with either 1 animal appearing on 2 occasions or 2 identical-looking animals each appearing once. The experimenter labeled each object appearance with a different novel label. After infants retrieved 1 object from the box, their subsequent search behavior was recorded. Twenty-month-olds, but not 16-month-olds, searched significantly longer for a second object inside the box when the labels were both proper names than when they were 1 count noun followed by 1 proper name. The effect was not significant when proper names were replaced by adjectives. Twenty-month-olds' understanding of meaning distinctions among several word categories guided their object individuation.