ABSTRACT. Recombinant human insulin-like growth factor I (rhIGF-I) has been produced in yeast and purified using conventional biochemical techniques. It has been shown to have receptor-binding properties and in vitro growth-promoting activities comparable to those of plasma-derived IGF-I. The anabolic actions of IGF-I can be studied using both systemic and local administration in vivo. The growth-promoting activity and systemic anabolic actions of recombinant IGF-I were studied in mutant dwarf rats. IGF-I was infused intravenously for 9 days and resulted in a significant gain in body weight and significant bone growth, though the effects were not as great as those observed with human growth hormone (hGH). IGF-I also had selective effects on specific organs which were not observed in hGH-treated animals. The results indicate that the growth-promoting effects of IGF-I show a different pattern compared to hGH. The effects of local administration of recombinant IGF-I on tissue regeneration and maintenance were also studied in hypophysectomized and normal rats. After hypophysectomy, the regeneration processes were impaired when both peripheral nerve regeneration and incision wound healing were considered. The results indicate that local administration could have significant effects on regeneration of, for example, peripheral nerves.