TL antigen was solubilized from the tumor ASLI (TL. 1,2,3) by papain digestion. The subfragments of 125I labeled TL were examined by two methods. The first involved immune precipitation followed by electrophoresis on SDS acrylamide gels. This treatment yielded three bands of molecular weight 39,000 and 19,000, as well as material which migrated with the tracking dye. In the second procedure the papain digested material was partially purified on Sephadex G 200. The active fraction from G 200 was labeled with 125Iodine, mixed with alloantiserum and rechromatographed on G 200. The isolated immune complexes were boiled in SDS and 2 mercaptoethanol, then separated on a SDS Sephadex G 150 column. Two radioactive peaks were eluted indicating an absence of the 19,000 m.w. component following the latter method of purification.