The relationship between the volume of fat flowing in the bloodstream and the degree of pulmonary fat embolism has remained unclear. In this study, in order to examine whether the volume of fat particles in the bloodstream could be estimated from the degree of pulmonary fat embolism, 0.05, 0.1, 0.15, 0.2 and 0.25 ml of triolein were injected into male rats weighing 300-320 g, through the caudal vein. Consequently, it was noted that the severity of pulmonary fat embolism tended to gradually increase in proportion to the volume of injected triolein, with the severity of pulmonary fat embolism being significantly augmented by the injection of 0.2 and 0.25 ml of triolein, based on morphometric analysis. In application to human cases, about 60 ml of fat particles was estimated to flow into the bloodstream after the occurrence of a pelvic fracture. Moreover, the results of this study led to the hypothesis that the prognosis of pulmonary fat embolism is affected by the severity of preceding conditions which have caused fat embolism.