The surface glycoproteins of the virally transformed rabbit T lymphocyte line, RL-5, have been studied by detergent lysis of metabolically radiolabeled cells followed by affinity chromatography on a variety of insolubilized lectins. Fractionation of the glycoprotein pool obtained from lentil lectin (LcH) by chromatography on Ricinus communis agglutinin (RCA) gives rise to two fractions. The first, which is not bound to the RCA column, contains mainly the major histocompatibility antigen, RL-A, as judged by gel electrophoresis, while the material which binds to the RCA column contains glycoproteins with apparent molecular weights greater than 70,000 daltons. This separation has been scaled up by the use of larger numbers of cells (10 to the 10th power or more) in order to obtain sufficient amounts of protein for amino acid sequence determination and for immunization of mice in order to raise hybridoma antibodies directed against the various cell surface glycoproteins.