Four groups of rabbits were exposed to either 4℃ (39℉) or −15℃ (5℉) for periods of from 1–10 weeks. It was observed that cold exposure of rabbits, even for short periods, altered the electrophoretic distribution of plasma proteins and the distribution of the formed elements of the blood. Increases were observed in the platelet and erythrocyte counts, hematocrit, plasma protein concentration, ß-globulins, fibrinogen, and in whole blood and plasma clotting times. The serum albumin concentration and prothrombin time decreased. Such alterations presumably reflect, or would be reflected in, modifications of the entire dynamic pattern of the animals' physiology. Many of these changes occurred very early (1 wk. at 4℃ in clipped animals), whereas, the effects of the most severe exposure used, 10 weeks at −15℃, were only slightly greater than at 4℃. It is suggested that the changes pass through a maximum and tend to return toward normal values. Submitted on November 7, 1957