Many of the present war problems on infectious diseases are concerned with the preparation of effective immunizing antigens, and involve the separation of antigenic substances from tissue or bacterial constitutents. Since the classical non-quantitative immunological approach is not always adequate, it seems desirable to review the literature of protein chemistry and immunology from the viewpoint of the immunochemist with special reference to the applicability of quantitative technics to the further elaboration of these problems. This survey will give a brief description of the quantitative methods of immunochemistry. It will then attempt a summary of the most recent contributions to our knowledge of a number of protein antigens and antibodies and point out how quantitative immunochemical technics may be useful in further studies when coordinated with the refined physicochemical technics of protein chemistry. The review will not consider the extensive and important studies on chemically altered proteins (Landsteiner and others (255) (e.g. azo-proteins) except when they relate directly to the specificity of the original native protein. 1