1. Pig thyroglobulin was reduced with dithiothreitol in the presence of sodium dodecyl sulphate, 8m-urea or 6m-guanidinium chloride. 2. The molecular weights of the reduction products were about 165000. 3. Two stable subunits with molecular weights as low as 35000 and 20000 were separated by Sephadex chromatography after prolonged exposure of the reduction products to sodium dodecyl sulphate at pH8.7. Although a hydrolytic reaction is probably implicated, the nature of the chemical linkages broken was not established.
