The effects of two types of stimuli, preferred and nonpreferred, on the free recall and clustering of 16 moderately and severely retarded public-school children were investigated. An empirical determination was made as to whether to classify a particular conceptual category of stimuli as preferred or nonpreferred. All subjects were presented with 18 objects from 6 conceptual categories in blocked condition. Both the preferred and nonpreferred stimuli were given to each subject in a counterbalanced order using a repeated measures design. Our major finding was that the use of preferred stimuli had a significant facilitating effect on recall but not clustering.