Rat monoclonal antibodies directed against the BALB/c myeloma protein M315 (alpha,lambda 2) are described. 9A8 (IgG1) binds the V domain of lambda 2 and cross-reacts with lambda 1 and lambda 3 chains. 2B6 (IgG2a) is directed to the C domain of lambda 2 and cross-reacts with C lambda 3. The antibodies bind isolated chains as well as complete immunoglobulins. The monoclonals detect soluble immunoglobulin (radioimmunoassay), immunoglobulin immobilized on polystyrene (enzyme-linked immunosorbent assay), immunoglobulin bound to nitrocellulose (immunoblotting), and surface immunoglobulin intercalated in cell membranes (immunofluorescence). The antibodies are easily purified on protein G immunosorbents and may be biotinylated or conjugated with fluorescein isothiocyanate without loss of capacity to bind. In addition to the anti-lambda antibodies, a C alpha 2/C alpha 3-specific monoclonal antibody, 8D2 (IgG2a) is described.