The changes in a number of haemostatic factors after fractures of the tibia or femur were compared with those observed in patients with fat embolism complicating such fractures. After fractures uncomplicated by fat embolism there was a rise in the fibrinogen, α₁-antitrypsin and serum activation inhibitor. The plasminogen level and platelet count initially fell, but later increased to above the initial levels. Patients whose fractures were complicated by fat embolism had the same pattern of changes but quantitatively greater.