1. Simultaneous platelet and fibrinogen survival studies were carried out on a group of seven normal persons and eleven diabetic patients. 2. Survival time was calculated: (a) by measuring the interval between 50% of the maximum radioactivity in the anabolic phase and 50% of the maximum radioactivity in the catabolic phase, and (b) by fitting an exponential function to the decay phase of the curve. 3. With the first method, the normal group had a mean platelet survival which did not differ significantly from that in the diabetic group. With the second method, however, the platelet half-life in the diabetic patients was significantly shorter than in the normal subjects. 4. Fibrinogen survival was significantly shorter in the diabetic group with either method. 5. It is concluded that there is an increased utilization of platelets and fibrinogen in diabetic subjects.