2,4,5,2',4',5'-Hexachlorobiphenyl (6-CB) is mobilized from rodent tissues during the lipid depletion associated with food restriction or lactation, the latter condition resulting in the substantial elimination of the maternal body burden of the chemical to nursing offspring. The present study was undertaken to determine whether the rate and/or magnitude of accumulation of 6-CB in nursing offspring differed with time following PCB administration to the maternal animal. Female ICR mice were administered two doses of 6-CB. Group I animals received [14C]-6-CB as weanlings (15-20 g) followed by unlabeled 6-CB 5 weeks later, after mating, on Day 1 of gestation. Group II received unlabeled 6-CB as weanlings and [14C]-6-CB on Day 1 of gestation. Thus, 14C identified the mobilization and elimination of either the first or the second dose of 6-CB in the treatment groups (I = [14C]-6-CB, 6-CB; II = 6-CB, [14C]-6-CB). Both groups of animals retained approximately 80% of the administered radiolabeled dose. The tissue distribution of [14C]-6-CB in group II as a percentage of the body burden was not different from that in group I as determined from maternal tissue concentrations on Day 14 of gestation. The percentage of the maternal body burden of [14C]-6-CB accumulated in suckling offspring of group II mothers was significantly greater than that in group I offspring on Day 1 (I, 2.2 +/- 0.5%; II, 3.5 +/- 0.4%), Day 3 (I, 14.8 +/- 1.9%; II, 24.6 +/- 2.7%), Day 5 (I, 16.8 +/- 1.4%; II, 24.8 +/- 0.8%), and Day 12 (I, 32.3 +/- 0.5%; II, 45.5 +/- 1.7%) postpartum. This differential elimination was reflected in the t1/2 of elimination of the radiolabeled dose from parametrial fat during lactation, which was significantly longer in group I (14 days) than group II maternal animals (9 days). The observations that the last dose of 6-CB administered was the first to be mobilized from the whole animal, and that this was reflected in 6-CB release from parametrial fat, suggest that this highly lipophilic chemical is not homogeneously distributed within storage depots.