It has been suggested based on fecal elimination data that a second dose of 2,4,5,2',4',5'-hexachlorobiphenyl (6-CB) is eliminated more rapidly from male rats than a first dose of 6-CB due to a differential accumulation of the two 6-CB doses within individual adipocytes. This phenomenon was further examined and extended to assess tissue levels of the compound in male rats which received either 0.6 mg/kg unlabeled or 14C-6-CB iv (dose 1). Fourteen days later, those animals which had received unlabeled 6-CB were administered 0.6 mg/kg 14C-6-CB. One-half of those rats which had received 14C-6-CB as dose 1 were administered unlabeled 6-CB after 14 days, and the remainder did not receive a second dose. The fecal excretion of radiolabeled 6-CB from rats treated only with 14C-6-CB was 5.3% of the total dose from days 14 through 28 post-treatment. Those rats receiving 14C-6-CB followed by unlabeled 6-CB excreted 4.4% of the total radiolabeled dose. Animals treated with 14C-6-CB as the second dose excreted 9% of their total radiolabeled dose within 14 days of treatment and those receiving only 14C-6-CB excreted 11% over the same time interval. Urinary elimination of radioactivity was negligible in all treatment groups. The pattern of distribution of 14C-6-CB in tissues was similar among all treatment groups. These data suggest that a second dose of 6-CB is not distributed differently from the first in growing male rats.