Cytochrome P450 enzymes (CYP enzymes) catalyse important metabolic reactions of exogenous and endogenous substrates, including steroid hormones. Here, we report the first two CYP sequences from the shore crab, Carcinus maenas. Two complete cDNAs isolated from crab hepatopancreas encode CYP enzymes named CYP330Al, the first member of a new family, and CYP4C39. CYP330Al is closest related to members of the CYP2 family (37.3%,, identical to mouse CYP2J6) and CYP4C39 is most identical to crayfish CYP4C15 (59.5%). CYP330AI gene expression was induced in hepatopancreas of male green intermoult crabs by ecdysone and ponasterone A, but also by benzo(a)pyrene and phenobarbital. CYP330AI induction was not observed in red crabs. The present results indicate that the CYP330AI enzyme may be involved in ecdysteroid metabolism, presumably catabolism, and in the detoxification of environmental pollutants. Ecdysteroids or xenobiotics did not affect CYP4C39 gene expression. The fact that both ecdysteroids and xenobiotics affect CYP330Al gene expression indicates that mutual interactions between chemical exposures and endocrine functions may exist in the shore crab. (C) 2003 Elsevier Inc. All rights reserved.