1. By use of our metallothionein (Mt) antibody in Western blotting and techniques for investigating protein metal-binding capacity, the form and content of Mt in bile, collected from cadmium (Cd) treated rats, were studied. 2. It was found that bile is an excretory pathway for Mt from the liver. 3. However, only immunoreactive proteins of higher molecular weight, probably representing polymerized forms of Mt or Mt bound to other proteins, were detected. 4. No monomeric Mt was found. 5. Excretion of Mt is probably not of importance in biliary metal transport.