Infant male Swiss mice (8 days old) were given a single i.p. injection of 500 mg/kg of the polychlorinated biphenyl (PCB) mixture, Aroclor 1254, a treatment found in previous studies to result in promotion of nitrosamine-initiated lung and liver tumors. The amounts of the nine congeners that account for > 90% of the PCBs still present 1 day after treatment were quantified in liver, lung, and remainder of carcass 1, 7, 56, 84, and 112 days after treatment. Rates of decrease (half-times, dt1/2s) for total PCB concentration and for individual congeners were compared within and between compartments and with body weight doubling time. In carcass (adipose compartment) there was net loss beyond that expected from dilution due to growth, with the predicted lower dt1/2s for the more metabolizable congeners. By contrast, in lung, after a rapid loss during the 1st week, all congeners except for #153 (2,2'4,4'5,5'-hexachlorobiphenyl [HCB]) were retained and decreased in amount only as a function of dilution due to growth. One result was that congeners #105 (2,3,3',4,4'-pentachlorobiphenyl [PeCB]) and #138 (2,2',3,4,4',5'-HCB) constituted a higher proportion in lung than in carcass. A complex pattern was observed in liver: relative to carcass, there was retention of all congeners during the prepubertal growth phase, again with specific enrichment of #105, followed by more rapid depletion of certain congeners later. PCB-binding proteins and changes in lipid composition may contribute to these phenomena, which are of human relevance in that these congeners are commonly found in human serum and adipose samples.