we examined the effect of long-term intermittent cold exposure (ce) on the fiber-type composition of the predominantly type i soleus and the predominantly type iib extensor digitorum longus (edl) muscles of the rats. ce was accomplished by submerging the rats in shoulder-deep water, maintained at 20 = 0.5 deg c, for 1 h/d, 5 d/wk, for up to 19 weeks. rats were randomly assigned to either a control (con) or cold exposure group. the efficacy of the treatment was tested by subjecting both groups to 20 deg c water for 45 minutes while measuring rectal temperature (tre) and v02. the ce group displayed a 22 smaller reduction in tre (p < 0.05) at the end of the exposure, and had a 23 greater v02 (p < 0-05) during the same period fiber-type composition was determined using routine histochemical methods for myosin-atpase. the soleus muscle of the ce rats underwent a 156 increase in the number of type iia fibers (p < 0.05), with a 24 reduction in type i fibers (p < 0.05). ce had no significant influence on the fiber-type composition of the edl muscle. ce resulted in an increase in citrate synthase activity of 20 and 22 in the soleus and edl muscles, respectively (p < 0.05). the present study demonstrates that intermittent ce induces a type i-to-type iia transformation in the soleus muscle while having no influence on the edl muscle