To clarify whether growth hormone possesses the counteracting effect on steroid myopathy, we examined the influence of simultaneous administration of recombinant human growth hormone (rhGH) with glucocorticoid on the diameter of muscle fibers in rats. Female Sprague-Dawley rats weighing 120-140 g were divided into four groups. A group treated with glucocorticoid alone was subcutaneously injected with 5 mg/kg/day triamcinolone, a GH-treated group with 10 IU/kg/day rhGH alone, a steroid-GH-group with the same doses of glucocorticoid and rhGH. The control rats were injected with the vehicle alone. After 14 days of treatment, each rat was anesthetized with ether and subjected to muscle biopsy of extensor digitorum longus (EDL) and soleus. Administration of rhGH alone failed to affect the diameter of muscle fibers in either EDL or soleus. Glucocorticoid treatment caused a significant reduction in the diameter of muscle fibers in the EDL, compared with the control. In the type II muscle fibers of the EDL, simultaneous administration of rhGH attenuated glucocorticoid-induced muscle atrophy significantly. We concluded that GH administration would at least partially prevents steroid myopathy.