The electrophoretic technic of Tiselius1 has been used by a number of workers to study the proteins in normal and in pathologic human serums.2 In this method, a boundary is formed in a specially designed U tube between a solution of proteins in a buffer and an ultrafiltrate of the solution. The application of a potential gradient across the boundary causes the original single boundary to separate into a series of boundaries corresponding to the number of electrophoretically discrete protein fractions present in the original mixture (certain anomalous boundaries being excluded). The boundaries move toward the electrode of the sign opposite the charge on the proteins forming the boundaries. By use of a lens system developed by Philpot,3 and later modified by Svensson,4 the positions of the boundaries can be visualized and the concentrations of the protein components determined. In short, the components of a mixture