Polychlorinated biphenyl (PCB) toxicokinetics andhepaticP450 (CYP) 1A activities werestudied in wild anadromous Arctic charr (Salvelinus alpinus) during winter emaciation. The fish were captured as they returned from summer feeding in seawater and were held without food over winter. In September the fish were given a single, oral dose of either 0 (control), 0.1, 1, or 50 μg PCB/g fish. During winter a net loss of PCB occurred from the carcass (including gut), whereas net inputs and increases in concentrations of PCB in the liver and brain occurred with increases in brain PCB concentrations being up to 10-fold. Hepatic CYP1A activities were positively correlated with the PCB dose in October. In the fish given 1 mg PCB/kg fish in September, however, a 12-fold increase in CYP1A activity occurred from October to May. This increase in CYP1A activity was observed during a period in which the body burden of PCB decreased by 20%. These results demonstrate that interpretations of the CYP1A biomarker response must be made with caution. Overall, the findings point to potentiated risks of biological effects of PCB during periods of emaciation.