Serologically and biochemically pure preparations of detergent and papain-solubilized HLA-A2 and HLA-B7 antigens were isolated by high pH elution from a series of immunoaffinity columns constructed from monoclonal antibodies with specificity for HLA-A2 and HLA-B7 antigens. These preparations retained the immunological activity and quaternary structure of the native molecule and should provide suitable reagents for insertion into liposomes and probing the role of major histocompatibility antigens in lymphocyte interactions.