The time course of muscular dystrophy on the androgen-sensitive levator ani muscle was compared to that of the diaphragm of dystrophic (mdx) mice aged 1-20 months. Muscle growth, isometric contractile properties and caffeine-induced contractures were determined to assess the hormone myotrophic effect, muscle strength and sarcoplasmic reticulum function, respectively, of both control and dystrophic muscles. Histological analysis of mdx muscles showed variable fiber size, centronucleated cells, infiltration of connective tissue, and necrosis which was less severe in the levator ani than in the diaphragm muscle. Tetanic tension per unit weight in the mdx levator ani was reduced (29%) after aging, while the contraction time remained unchanged. The tetanic tension of the mdx diaphragm muscle decreased with age from 3 to 20 months (20-64%), and the relaxation time was prolonged after aging (22%). Gonadectomy of young adult mdx mice caused atrophy of the levator ani muscle, accelerated muscle wasting, reduced the tetanic force (31%), but it did not affect the contraction time and caffeine responses. The results showed that testosterone does not prevent the progress of muscle disease in the mdx levator ani, but androgen withdrawal accelerates muscle wasting suggesting a normonal beneficial effect.