The ability of an association of three steroid hormones to influence the reinnervation process and the trophism of rabbit muscles denervated by crush of the sciatic nerve was investigated. The beginning of reinnervation was established with electromyographic recordings from the tibialis anterior muscle. The distance from the site of crushing to the point where the motor nerve enters the tibialis anterior muscle was then measured in each animal, and the nerve regeneration velocity (mm/day) was calculated: a slightly but significantly higher (P less than 0.001) mean value was found in treated animals compared with untreated ones. When soleus and extensor digitorum longus (EDL) muscles were histochemically examined 50 days after lesion, a larger mean diameter of type 2c fibers was found in treated than in untreated animals, pointing out a possible useful effect of the treatment. On the contrary, the size reduction of EDL type 2b fibers was more pronounced in treated rabbits, indicating a catabolic influence of the drugs on this fiber type.