1. 2,3,7,8-Tetrabromodibenzodioxin was administered to bile-duct-cannulated rats in a single oral dose. 2. The compound was metabolized in the liver and metabolites were secreted into the bile. 3. Several phenolic metabolites were identified as their methyl ether derivatives by gas chromatography-mass spectrometry after clean-up and methylation of bile samples. 4. The main metabolites were formed by aromatic hydroxylation and via displacement of Br-substituents (hydrolytic debromination). 5. Trace amounts of unmetabolized TBDD were also present in the bile.