A physiologically based pharmacokinetic model is developed that describes the uptake and release of a hydrophobic organic chemical by a marine mammal over its entire lifetime, i.e., from birth to death. This model is applied to polychlorinated biphenyls (PCBs) in the beluga whale (Delphinapterus leucas). The processes treated are growth; uptake from food, milk, and air; disposition of the chemical among arterial and venous blood, liver, muscle, blubber, and rapidly perfused tissues; and losses by metabolism, release in exhaled air, and by egestion. A separate model is developed for females, which includes pregnancy, birth, and lactation. Food consumption is deduced from size, growth, and from activity-dependent bioenergetic data. The results obtained by simulating continuous PCB exposure over a 30-year period are in accordance with reported concentrations and show the importance of milk transfer to both mother and progeny and the tendency for continued accumulation over the animal's lifetime. Implications of the results are discussed, especially the need for improved data on diets, gut absorption characteristics, and various physiological parameters used in the model.