Three experiments are reported which investigated the relationship between stimulus organization and performance in classification tasks. In Experiment 1, a conjunctive solution involving proximate stimuli was learned more rapidly than a solution involving nonproximate stimuli. In Experiments 2 and 3, type of solution (similar stimuli vs nonsimilar stimuli in Experiment 2; and unique vs nonunique stimuli in Experiment 3) and number of dimensions had interaction effects on rate of learning. © 1969, Psychonomic Journals, Inc.. All rights reserved.