Serological techniques involved the extraction of saline-soluble proteins from the tissues of the species to be studied. These extracts were carefully processed and were used as antigens. Formolization of the antigens was necessary as a means of preventing denaturation of the proteins by enzymatic activity. Antisera were produced in rabbits. The method of testing involved turbidimetric analysis of the precipitin reaction. Utilizing the values for the precipitin tests a model was constructed which showed the relationships of the eleven species used in these tests. From a study of the model and the data used in its construction, it was determined that the Richmondeninae, Emberizinae, and Thraupidae constitute an assemblage distinct from the other species studied. The Carduelinae are excluded from the assemblage and serologically are most closely related to the Estrildinae. The estrildines, serologically, do not closely resemble _Passer_, Subfamily Passerinae, although recent classifications place these two subfamilies in the Family Ploceidae. Upon consideration of all evidence now available--from external morphology, ethology, myology, osteology, and serology--several hypotheses regarding the relationships of the groups studied are set forth. The richmondenines, emberizines, and tanagers are closely related subfamilies and are here included in the Family Fringillidae. The Estrildinae and Carduelinae are closely related subfamilies, but neither group is closely related to the Passerinae. The estrildines and carduelines, therefore, are placed in a separate family, the Carduelidae. In some ways, _Spiza_ is an aberrant member of the Subfamily Richmondeninae but should be retained in that subfamily. It is suggested that _Spiza_ is a primitive richmondenine closely related to the ancestral fringillid stock. LITERATURE CITED AMERICAN ORNITHOLOGISTS' UNION 1931. Check-list of North American birds. Fourth edition. Lancaster, Pa., xix + 526 pp. BEECHER, W. J. 1951a. Adaptations for food-getting in the American blackbirds. Auk, 68:411-440, 11 figs. 1951b. Convergence in the Coerebidae. Wilson Bull., 63:274-287, 5 figs. 1953. A phylogeny of the oscines. Auk, 70:270-333, 18 figs. BERGER, A. J. 1952. The comparative functional morphology of the pelvic appendage in three genera of Cuculidae. Amer. Mid. Nat., 47:513-605, 29 pls. BOYDEN, A. 1942. Systematic serology: a critical appreciation. Physiol. Zool., 15:109-145, 12 figs. CHAPIN, J. P. 1917. The classification of the weaver-birds. Bull. Amer. Mus. Nat. Hist., 37:243-280, 10 pls., 9 figs. CUMLEY, R. W., and IRWIN, M. R. 1941. Pictorial representation of the antigenic differences between two dove species. Jour. Hered., 32:178-182, frontispiece, 2 figs. 1941. Interaction of antigens in dove hybrids. Ibid., 429-434, 3 figs.