It has been shown that all-trans retinoic acid induces prematurely hepatic glucokinase mRNA in ten days-old neonatal rat hepatocytes, however, this effect could be related to the capacity of the retinoid to promote a more differentiated state of the hepatocyte. In this report we demonstrate that physiological concentrations of all-trans retinoic acid stimulate glucokinase activity in both mature fully differentiated hepatocytes and at the onset of the induction of the enzyme in 15 to 17 days-old neonatal hepatocytes. The effects produced by the retinoid were similar both in magnitude and in time, to those elicited by insulin, a well-known stimulator of hepatic glucokinase expression. No additive effect was observed when insulin and retinoic acid were tested together. Using the branched DNA assay, a sensitive signal amplification technique, we detected relative increases in glucokinase mRNA levels of about 70% at 3 and 24 h after the treatment with 10(-6) M all-trans retinoic acid, in both neonatal and adult hepatocytes. These data show that retinoic acid exerts a stimulatory effect on hepatic glucokinase independent of the hepatocyte stage of maturity and suggest a physiological role of retinoic acid on glucose metabolism. The action of retinoic acid on hepatic glucokinase might explain previous observations on the relationship between vitamin A status and liver glycogen synthesis. These findings may serve as basis for further investigations on the biological functions of retinoic acid derivatives on hepatic glucose metabolism.