Polybrominated dibenzo-p-dioxins and dibenzofurans are of major concern because of potential occupational and environmental exposures and their structural similarity to the highly toxic chlorinated analogues. 2,3,7,8-Tetrabromodibenzo-p-dioxin (TBDD) is a closely related analogue in both structure and activity to the most toxic isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin. The objectives of this study were to characterize the effects of dose and routes on absorption, excretion, and terminal tissue distribution of (3H)TBDD in the rat 72 hr after dosing. The major tissue depots of radioactivity were liver, adipose tissue, and skin. Tissue distribution of the oral dose was dose-dependent, with disproportionally greater hepatic concentrations occurring at absorbed doses of > 8 nmol/kg. Liver:adipose tissue (L:F) concentration ratios were 2.9 to 6.6 (lowest to highest oral dose, respectively). The lower L:F ratios observed for the dermal and intratracheal doses at 1 nmol/kg (1.5 and 2, respectively) were likely due to differences in absorbed dose and dose-related tissue distribution.