TO EXAMINE THE effects of aging on recovery from disuse muscular atrophy, the following experiments were performed. Using young (12w) and old (50w) female Wistar rats, a muscular atrophy model was produced by nonweightbearing of the bilateral hindlimbs by tail suspension and fixation of the ankle joint in one hind limb for 2 weeks, and the recovery course was examined. Free walking was allowed for 0-6 weeks after the removal of tail suspension and joint fixation, and measurement of the wet weight of muscles and histological examination were performed 0, 2, 4, and 6 weeks after the start of walking with four limbs. There was no difference in the degree of atrophy in the fixed soleus between the young and old rats. The recovery from atrophy was delayed in the old rats as compared to the young rats. In the unfixed hind limb, the degree of atrophy was low in both the old and young rats, and recovery was rapid. Because disuse muscular atrophy is prolonged with aging, it is necessary for elderly people, in particular, to avoid the condition of nonweightbearing and immobilization.