The purpose of this study was to investigate alterations in his tochemical properties in the gastrocnemius & soleus muscles of rats following hindlimb suspension for 1 week. A modification of the Morey and Musacchia models was used to determine atrophic responses of rat muscle. The weights of rat's whole body and of gastrocnemius and soleus muscles were affected by suspension. A reduction of type I distribution was accompanied by an increase in type II fibers. The cross sectional area of all fiber types was reduced after suspension. These results suggest that type I fibers showed greater susceptibility than type II fibers and some amount of type I fibers might have been converted to type II fibers.