The effects of negative instances in the acquisition of the conjunctive concepts of distributivity and homomorphism were examined. Ninety-two elementary education majors were used as subjects. Two treatment levels for distributivity (series of positive instances or positive and negative instances) and the same treatment levels for homomorphism were crossed to form a 2 x 2 factorial design with 23 subjects per cell. Criterion variables were number of correct classifications, stimulus intervals, and postfeedback intervals. All pretests, treatments, and posttests were administered using computer terminals. The results supported the hypotheses that negative instances enhance conjunctive concept acquisition and that effects of negative instances for one concept transfer to another concept. (Author/DT)