Hepatic cytochrome P-450 (CYP450) isozymes are involved in xenobiotic detoxification and steroid metabolism. Seals are highly exposed to polychlorinated biphenyls (PCBs) in the environment, resulting in CYP450 induction, which may have concomitant effects on CYP450 steroid metabolism. Experiments were conducted to determine rates of steroid metabolism in harbor seal (Phoca vitulina