The electrophoretic mobilities of different prepns. of serum globulin were measured by the author''s moving boundary method. Phosphate and acetate buffer solutions of varying pH but constant ionic strength 0.1 were used as media. The isoelectric points for unfractioned horse and rabbit serum globulins were pH 5.2 and 5.26, and the slope of the pH-mobility curve du/dpH at the isoelectric points 4.3 X 10-5 and 4.6 X 10-5, respectively, at 20[degree]. No appreciable difference was found between pseudo-and euglobulin; both showed a somewhat lower mobility than whole globulin at alkaline pH.