Each of five male and five female rats was orally dosed with 49.2 mug 2,2'-dichlorobiphenyl-14C daily for 42 days. After 36 days, the radioactivity in the body reached a plateau level, and male rats had excreted 84.5% of the applied radioactivity, females 87.9%; the residues in most organs were below 0.2 mg/kg. The daily excreted radioactivity after 50 days had decreased to 0.7% (males) and 0.5% (females) of the daily dose; the total excretion was then 86.2% (males) and 89.4% (females) of the total applied dose, and the organs contained less than 0.1 mg/kg. More than 90% of the radioactivity in the excreta was due to metabolites (one monomethoxy-, three monohydroxy-, three dihydroxy-, one trihydroxy-2, 2' -dichlorobiphenyl, conjugates, and a dechlorinated derivative).