The expression of CYP1A (cytochrome P4501A) can be induced by a number of aromatic compounds in teleost fishes. We developed a real-time PCR assay for measuring relative quantities (RQ) of CYP1A mRNA in whitefish (Coregonus lavaretus). To test for the usefulness of the assay we performed a treatment study, using benzo[a]pyrene (B[a]P) a model CYP1A inducer. Primers for the CYP1A gene were adapted from the literature, whereas those for [beta]-actin (endogenous control) were designed from a region that was found to be conserved among salmonid [beta]-actin genes. A group of hatchery raised whitefish, with an average body mass of 15 g and total length of 12 cm were given an intraperitoneal injection (10 mg/kg) of B[a]P in corn oil (2 mg B[a]P/ml corn oil) or corn oil alone (Control). After 48 h, whitefish liver, head kidney and brains were collected for mRNA isolation and analysis. In all three tissues sampled, CYP1A mRNA was affected by treatment with B[a]P. Head kidney tissue showed the greatest induction potential (RQ=11.00) from base levels (RQ=1.00), followed by liver (RQ=9.45), and brain (RQ=3.76). These results demonstrated that CYP1A was highly inducible by B[a]P in whitefish head kidney and liver, and to some extent, in brain tissue. The approach presented here has the advantage of providing rapid and accurate measures of CYP1A induction in various tissues of fish responding to PAH contaminant exposure.