DDT, dieldrin, and PCB contents of tissues and the sucking lice of the northern fur seal (Callorhinus ursinus) were studied in samples collected in July 1972 in the Pribilof Islands, Alaska. They included the analyses of two nursing cows and their two newborn pups, three 2-month-old pups, and the sucking lice inhabiting these animals, Antarctophthirus callorhini and Proechinophthirus fluctus. The sigmaDDT content of fat tissue was 5.2, 5.6 and 63 mug/g (-/x) for cows, newborns, and 2-month-old pups, respectively. Dieldrin appeared at trace levels. PCB residues (Aroclor 1254) were 5.8, 5.5, and 33 mug/g (-/x), respectively. The sigmaDDT content of blood was less than 0.01 mug/g for cows and newborns and 4.6 mug/g for 2-month-old pups. PCB's were found only in trace amounts in the blood of all animals except one 2-month-old pup which contained 3.4 mug/g. Lice contained 0.2-6 percent, respectively, of the sigmaDDT and PCB's detected. All residues were expressed on a wet-weight basis. Two-month-old pups had far higher residue levels than had cows. A high percentage of sigmaDDT occurred as the DDE metabolite: 60 percent in cows and newborn pups and 90 percent in 2-month-old pups.