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Abstract: We previously reported in vivo induction of cytochrome P450 1A (CYP1A) by β-naphthoflavone in skin and liver biopsies of captive harbour seals (Phoca vitulina richardsi). The present study evaluated CYP1A expression (immunoblot analysis and ethoxyresorufin O-deethylase activity-EROD) in harbour seals using two study designs: i) skin and liver biopsies from 20 harbour seal pups captured from coastal British Columbia (BC, Canada) and temporarily housed in captivity; and ii) skin biopsies from 42 free-ranging harbour seals captured and sampled on-site in multiple locations in BC and Washington State (USA). Toxic Equivalency Quotients (TEQs) were calculated for polychlorinated biphenyl, polychlorinated dibenzo-p-dioxin, and polychlorinated dibenzofuran residues measured in blubber from a subset of study animals (n =30). CYP1A data from the seal pups held temporarily in captivity show that CYP1A protein levels were greater in liver than skin and that CYP1A protein and EROD activity were correlated in skin and liver. However, analysis of free-ranging seals from different sites revealed that blubber organochlorine TEQ values did not correlate with skin CYP1A levels. CYP1A protein levels and EROD activities in skin of seal pups from the BC locations and from Puget Sound were relatively low, possibly reflecting contaminant levels that were not high enough to elicit a response, a small sample size, or methodological limitations. Our results show that CYP1A measurements in skin show promise as a biomarker of contaminant exposure, but that refinements to techniques and a larger sample size are needed. [Copyright &y& Elsevier]