The effect of insulin-like growth factor I (IGF-I) on the activity of alcohol dehydrogenase was determined in primary hepatocyte culture from male rats. Continuous exposure of hepatocytes to IGF-I (30 nM) resulted in increases in alcohol dehydrogenase activity on Days 3-6 of culture. The increase in enzyme activity was preceded by increased alcohol dehydrogenase mRNA, indicating that the effect of IGF-I was at the pretranslational level. The effect of IGF-I was observed only in the presence of pharmacological concentrations of insulin in the media. Insulin alone had no effect on alcohol dehydrogenase activity. The permissive influence of insulin was correlated with the ability of insulin to maintain a steady high number of IGF-I binding receptors in the hepatocytes during culture. The response of alcohol dehydrogenase to IGF-I is similar to that previously demonstrated for growth hormone and suggests the possibility that the effect of growth hormone on this enzyme may be mediated by IGF-I.