Marine mammals can bioaccumulate high concentrations of lipophilic environmental contaminants, such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-para-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs), through the diet. Both laboratory and wildlife studies have shown that these persistent chemicals can disrupt the regulation of vitamin A (retinol), a dietary hormone required for immune function, reproduction, growth, and development. To determine whether environmental contaminants affect the circulatory vitamin A dynamics of free-ranging harbor seals (Phoca vitulina), we live-captured 61 pups from British Columbia, Canada, and Washington State, USA, and obtained blood and blubber biopsy samples. Harbor seal pups from Washington State were six times more contaminated with total PCBs than pups from British Columbia and had significantly lower circulatory retinol levels. However, when data were corrected for differences in nursing status and analyzed as ungrouped sets of data, circulatory retinol levels were positively correlated with contaminant levels in the blubber of nonnursing pups. This increase in retinol may have resulted from a mobilization of liver vitamin A stores into circulation following exposure to milk-derived contaminants; this has been observed in laboratory animals exposed experimentally. The contaminant-related disruption of vitamin A dynamics observed in our study occurs at a time when vitamin A is required for growth and development.