The effects of exercise intensity on the stereotypic behaviors of three subjects with autism were examined. Two exercise programs of different intensities were implemented. The mild exercise program involved 15 min of walking, and the vigorous program involved 15 min of jogging. The frequency of stereotypic behavior was measured prior to exercise, immediately following exercise, and 90 min following exercise. The results indicated that significant reductions in stereotypic behaviors occurred as a function of the vigorous exercise condition only. The mean reduction of stereotypic behaviors between prejogging and postjogging was 17.5%. However, the duration of these reductions was temporary. Increases to preexercise levels were noted in stereotypic behaviors 90 min after exercise. The stereotypic behaviors of subjects were categorized into three components: motor, vocal/oral, and other. The motor component was most common. The mild exercise condition had little effect on the motor component; the vigorous condition resulted in a mean reduction of 17%.