Four experiments investigated the influence of categorization training on perceptual discrimination. Subjects were trained according to one of four different categorization regimes: Dimension X relevant, Dimension Y relevant, Dimensions X and Y relevant, and no categorization training. Subsequent to category learning, subjects performed a perceptual aSame"/"Different" judgment task. Subjects' sensitivities (d') for making three types of discrimination were measured: discriminations between items that varied on a categorization-relevant dimension but belonged to the same category, discriminations between items that varied on a categorization-relevant dimension and belonged to different categories, and discriminations between items that varied on an irrelevant dimension. When separable dimensions were used, evidence for acquired distinctiveness (increased perceptual sensitivity for items that are categorized differently) was obtained, and one case of acquired equivalence (decreased perceptual sensitivity for items that are categorized together) was found. With integral dimensions, evidence for acquired distinctiveness was obtained, but no evidence for acquired equivalence was found. Acquired equivalence within a categorization- relevant dimension was never found for either integral or separable dimensions. The relevance of the results for theories of perceptual learning, dimensional attention, categorical perception, and categorization are discussed.