IGF I and IGF II are insulin-like peptide hormones circulating in blood bound to specific carrier proteins. IGF I mediates many actions of growth hormone--hence its designation as somatomedin C--and it stimulates cell replication, cell differentiation and the synthesis of cellular products (matrix proteins, etc.). Recent investigations in normal human subjects show that pharmacological doses of IGF I increase renal function and have profound metabolic effects that might prove to be useful in the treatment of conditions characterized by relative insulin resistance, such as type 2 diabetes, obesity and hyperlipidemia.