Expression of growth hormone receptor mRNA was investigated by in situ hybridization in skeletal muscle from normal and hypophysectomized rats during the first seven days of regeneration after ischemic injury. A digoxigenin-labelled RNA probe directed against the extracellular part of the rat GH receptor was used. In both normal and hypophysectomized rats distinct expression of GH receptor mRNA could be demonstrated in the regenerating muscle cells at the myoblast/myotube stage. The GH receptor expression appeared to decline with increasing maturation of the regenerated muscle fibres. In hypophysectomized rats, the regeneration process and the expression of GH receptor mRNA was delayed compared with that in normal animals. It is concluded that growth hormone may affect also the early phase of muscle regeneration in normal animals. To what extent lack of growth hormone contributes to the delayed regeneration observed in the hypophysectomized rats remains to be elucidated.