A study was made on the effects of recombinant human growth hormone (rhGH) on fast and slow skeletal muscle in normal adult female rats. Daily injections of 4 IE of rhGH over 36 days resulted in increased levels of insulin‐like growth factor I in serum and increased body weight. Morphometric analysis of the muscle fibres of the extensor digitorum longus (EDL) and soleus muscles revealed a significant increase in diameter of both type 1 and type 2 fibres in both muscles. The DNA: protein ratio and the number of satellite cells: muscle fibre in cross‐sections was increased in the GH‐treated rats in relation to controls. The results show that rhGH has pronounced effects on both cell proliferation and muscle fibre growth in skeletal muscle of normal adults rats.