Ia antigens were previously shown to be B-cell receptors for transformed cell surface glycoproteins (TCSG). Ia antigen recognition of TCSG subsequently initiated interferon production. These findings have been exploited to highly purify TCSG from mouse L (H-2k) cells in one step by Ik antigen Sepharose affinity chromatography. These results point to the highly specific recognition of TCSG by Ia antigens and the B-cells on which they reside. The implications and applications of these Studies are discussed. © 1986, SAGE Publications. All rights reserved.