Chromatographically purified human IgG1 lambda, allotype G1m(f). Purified human IgG1 lambda may be used as a reference antigen, calibrator, coating protein and blocking agent in a variety of immunoassays including immunodiffusion, immunoelectrophoresis, ELISA, Western blotting, dot-immunobinding assays (DIBA), haemagglutination, and cell-binding assays.