The effects of a seven-month aerobic-type exercise program on physical fitness and intelligence of institutionalized adult mentally retarded persons were evaluated. Sixty-five subjects, matched on IQ, CA, and sex, were assigned randomly to exercise (PF), attention control (AC), and nonintervention control (C) groups. PF and AC groups participated in 139 training sessions, three hours per day, five days per week. The exercise consisted of running/jogging, calisthenics, and circuit training; those in the AC groups received a special education program; the C group continued their normal institutional training programs. Cardiovascular efficiency improved in the PF group. IQ and adaptive behavior did not improve as a result of any treatment. Even though standardized tests reflected little change in adaptive behavior of participants, subjective reports suggest PF training may serve as an effective habilitation program for many institutionalized mentally retarded adults.