Type 2C muscle fibers were histochemically and biochemically examined under three different conditions in rats: in the neonatal stage, after neonatal denervation and on regenerating process after bupivacaine-induced injury. On histochemical examination, soleus was found to contain up to 90% of type 2C fiber in every condition, whereas both gastrocnemius and extensor digitorum longus contained 40-70%. On biochemical analysis, triglyceride was the smallest and glycogen was the largest in amounts in neonatal muscles, triglyceride was the largest and glycogen was lowest in amount in neonatal denervated muscles, while both triglyceride and glycogen were low in amounts in bupivacaine-treated muscles. These results suggested that although histochemical characteristics are the same, significant differences in biochemical properties exist between type 2C fibers in these three different conditions.