Recombinant DNA technology has made large amounts of insulin-like growth factor-I (IGF-I) available for studies in animal models and humans. It has been shown that treatment with IGF-I is associated with increased insulin sensitivity in normal subjects as well as in patients with growth hormone deficiency, Type 1 and Type 2 diabetes mellitus and type A insulin-resistance. The metabolic effects of IFG-I appear to be beneficial in these conditions. The reported side effects of IGF-I, which may be largely due to overdosage, have limited its use to small and mostly short-term clinical studies.