The numbers of fat macroglobules in peripheral venous blood were recorded for 136 prospectively studied patients with fractures of the pelvis, femur, or tibia. Groups of healthy volunteers and patients undergoing total hip replacement or abdominal surgery served as controls. The highest incidence of fat macroglobulemia occurred in patients with fractures of the femur who also had these clinical signs: petechiae, hypoxia, and depression of the central nervous system. The peak incidence occurred within the first eight hours after fracture. The over-all incidence of fat macroglobulemia in the other surgical patients was roughly equivalent to that in the fracture patients.