Summary1. A study of 81 electrophoretic patterns of serum of diabetic patients shows a high frequency of protein disturbances, of which the most constant are a decrease in the amount of albumins and an increase in the amount of and especiallyftglobulins.2. In the uncomplicated diabetic and especially when the disease is benign, as in obese adults, the protein disturbances are relatively slight. In the forms more serious there is a clear increase of the electrophoretic anomalies : selective increase of the a2globulins in the juvenile diabetes; a marked decrease of the albumins and a considerable increase of theftglobulins in diabetic adults with severe weight loss.3. The protein alterations exist already in the course of the first months or years of the disease. If the disease is not complicated by degenerative lesions, only the hypoalbuminemia seems to increase in the course of the evolution of the diabetes.4. The age of the patient intervenes in these protein modifications in predisposing adult subjects to a decrease of the albumins and to an increase of theftglobulins.5. The appearance of vascular complications exaggerates simultaneously the decrease of the albumins and the increase of the amount of a2andßglobulins. The Kimmelstiel-Wilson syndrome is especially characterized by a decrease in the albumins and a considerable increase in a2globulins.6. Infections and pregnancy modify the electrophoretic picture in the same manner as in subjects non-diabetic.7. In the case of severe hemochromatosis the electrophoretic pattern shows a normal or even a decreased amount offtglobulins.8. At this time the interpretation of these anomalies can only be hypothetical. The hypoalbuminemia seems to result either, from a trouble in synthesis by the liver, or from an exaggerated protein catabolism. The hyperglobulinemia a2could be interpretated, in certain special pathological conditions (hyalinosis) to an augmentation of the level of serum polysaccharides. The increase of theftglobulins signifies probably an enrichment of the serum in lipoproteins of high molecular weight to which one attributes an«atherogenic»role.