Fetal rat or neonatal human hepatocytes and a human hepatoma cell line were cultured in an arginine-free medium, supplemented or not with L-ornithine. This amino-acid improved survival of hepatocytes and strongly enhanced their transferrin secretion. Moreover, this increase observed in transferrin production was well correlated with a higher corresponding mRNA level. Thus, it may be postulated that the mechanism involved in the increased transferrin secretion by L-ornithine is of pretranslational origin.