The aim of this study was to compare features of muscle atrophy induced by cast fixation. denervation and suspension of rat hindimb. Muscle mass and glycogen of the soleus and plantaris muscles were studied after 3, 7, or 14 days of cast fixation, denervation and suspension. The results as follows: 1. Body weight of rats decreased significantly after 3 days and showed gradually increase after 7 and 14 days of hindlimb cast fixation, denervation and suspension. Particularly hindlimb suspended rats showed a rapid decrease after 3 days in body weight. 2. Relative weight of soleus and plantaris musclcs decreased significantly by hindlimb cast fixation, denervation and suspension, particularly after 7 days. The decrease rate was the lowest in suspended rats. 3. Glycogen content of soleus muscle decreased significantly after 14 days of hindlimb cast fixation, denervation and suspension. Also glycogen content of plantaris muscle decreased significantly after 14 days of hindlimb cast fixation and denervation, but not significantly after hindlimb suspension. These results indicate that suspension of hindlimb muscles causes less atropy than cast fixation or denervation, likely due to maintainment a few activities during hindlimb suspension. We concluded that the decrease in mechanical strains imposed on the muscle during inactivity was the main factor for the development of atrophy. These basic data suggest that some experimental conditions such as electrostimulation or stretching, participate in countermeasure programmes.