An immunochemical analysis of the Ly-8.2 antigen was performed. Reactivity of B10-radiolabeled T and B cell lysates with a C3H anti-AKR serum immunoprecipitates a major 43,000 m.w. protein detectable by one-dimensional gel electrophoresis. The protein can be radioiodinated, however, it does not appear to blind to lentil lectin. Two-dimensional gel electro phoresis and peptide-mapping studies indicate that this protein is structurally very similar to lymphocyte actin. The possible molecular relationship between Ly-8.2, other lymphocyte membrane antigens, and actin is discussed.