Twenty-four patients with muscular dystrophy carried out a maximum resistance exercise program for one year. Improvement in muscle strength occurred in all patients throughout the first four months of exercise regardless of type of dystrophy. Subsequently, a plateau occurred which was maintained throughout the period of observation. The increased muscle function as documented by objective measurements was correlated with the initial level of muscle function. Improvement in functional abilities was less than increase in muscle strength. Patients with "limb-girdle" and facioscapulohumeral dystrophy derived the greatest physical and functional benefit from the program. A resistive exercise program in muscular dystrophy is most effective if instituted early in the course of disease.