Black guillemots (Cepphus grylle) in Saglek Bay, Labrador have elevated polychlorinated biphenyl (PCB) concentrations due to marine sediment contamination around a former military site. We measured liver biomarkers and sigmaPCB concentrations in 31 nestlings from three PCB-exposure groups: Reference group (range: 15-46 ng/g liver, wet wt.), moderately exposed Islands group (24-150 ng/g), and highly exposed Beach group (170-6200 ng/g). Biomarker responses were dose-dependent and in some cases sex-dependent. Livers of female Beach nestlings were enlarged 36% relative to Reference females. In both sexes, Beach nestlings had liver ethoxyresorufin-O-deethylase (EROD) activities elevated 79% and liver retinol concentrations reduced 47%. Retinyl palmitate concentrations were reduced 50% but only among female nestlings. Island nestlings also exhibited EROD induction (57%) and reductions in retinol and retinyl palmitate concentrations (28 and 58%, respectively). Liver lipid content increased with sigmaPCBs in both sexes, and correlated with liver mass in males. Malic enzyme activity and porphyrin concentrations showed little association with sigmaPCBs. Although similar associations between liver biomarkers and organochlorine exposure in fish-eating birds are well documented, typically exposures involve multiple contaminants and there is uncertainty about specific PCB effects. Our findings indicate that liver biomarkers respond to relatively low PCB exposures (approximately 73 ng/g liver) in guillemots.