Octachlorodibenzo-p-dioxin (OCDD) is a widespread environmental contaminant which has been reported to be nontoxic after acute administration. The disposition of [¹⁴C]OCDD was studied in male Fischer 344 rats in order to better assess the significance of chronic environmental exposure to OCDD. Rats were treated with 50 μg OCDD/kg iv, and 50, 500, or 5000 μg/kg po and held in individual metabolism cages for 3 days. Additional rats treated iv were held up to 56 days to follow elimination of OCDD-derived radioactivity and to determine terminal tissue distribution. Feces was the major route of elimination after both routes of exposure with little radioactivity ever appearing in the urine. Gastrointestinal absorption was nonlinear between 500 and 5000 μg/kg, never exceeding 10% of the administered dose. Liver was the major depot, followed by adipose tissue and skin. No metabolites of OCDD were detected in tissues, bile, or excreta. The whole-body half-life for the elimination of OCDD was between 3 and 5 months. Repeated oral exposure resulted in linear accumulation of OCDD in the tissues. Thus, OCDD, while poorly absorbed, can accumulate upon low-dose, repeated exposure and concentrate in the liver and adipose tissue.