SummaryA case of myelomed of which blood contains 53 gr % of cryoglobulin is described. The authors stress the characteristic clinical signs of this disease : acrocyanose, sensitivity to cold, alteration of the fundus.These symptoms are due to the presence in blood of an abnormal protein. This induces an important rise of the plasma viscosity at 37°, which still increases when the temperature decreases. This cryoglobulin slows the circulation in peripherical cutaneous territories affected by variations of temperature. A study of the plasma viscosity has been made at different temperatures. Some aspects of this solubility of cryoglobulin have been discussed. Hemodynamic observations suggest that circulation in deep territories is practically normal.