To assess the effects of the polycyclic aromatic hydrocarbons (PAHs) beta-naphthoflavone (beta-NF) and benzo(a)pyrene (BaP) on liver intermediary metabolism and plasma steroid hormones, immature female rainbow trout (Oncorhynchus mykiss) were intraperitoneally injected (2 microl g(-1)) with vegetable oil alone (control) or containing beta-NF or BaP (10 mg kg(-1)) and returned to their tanks; 3, 24, and 72 h after injection, 11 fish were sampled from each group. On each sampling time, plasma hormone levels (cortisol and 17beta-estradiol) and metabolic parameters in plasma (glucose, lactate, and alpha-amino acid levels) and liver (glycogen, glucose, lactate, and alpha-amino acid levels, and HK, GK, PK, LDH, G6Pase, G6PDH, FBPase, GDH, Asp-AT, and HOAD activities) were assessed. Changes described for hormonal systems resulted in an increase in plasma levels of cortisol after 24 and 72 h of treatment with both PAHs whereas no changes were noticed for 17beta-estradiol levels. Changes in intermediary metabolism described effects in several pathways due to treatment with both PAHs. These changes can be summarized as increased glucose and lactate levels in plasma, and increased glycogenolysis and gluconeogenesis in liver after 24 and 72 h of treatment with both PAHs. Furthermore, beta-NF treatment stimulated amino acid catabolism in liver. These metabolic changes can be associated with increased levels of plasma cortisol, and suggest a different metabolic behavior depending on PAHs.