Primary hepatocyte culture is a valuable tool for studies on regulation and function of the cytochrome P450-dependent enzymes, since such a system provides conditions close to biochemical and physiological responses of liver cells in intact animal. Previous works have shown that cytochrome P450-dependent activities and their induction by known inducers, such as beta-naphthoflavone (betaNF), could be measured in primary culture of rainbow trout hepatocytes. Furthermore, recent studies have demonstrated that glucocorticoids (GC) potentiated the induction of cytochrome P4501A1 by polycyclic aromatic hydrocarbons (PAH) in mammals. Our results show that induction of ethoxyresorufin-O-deethylase (EROD) activity by betaNF is potentiated by dexamethasone (DEX) or cortisol in trout hepatocyte cultures. Since glucocorticoid levels can increase in fish exposed to pollutants, such steroids may interfere with the induction response to xenobiotics.