According to some investigators, trauma is thought to bring about physical changes which produce a coalescence of normally dispersed blood lipids into fat droplets and pulmonary fat embolisms. Lipemia is thought to increase the extent of this embolization. If this theory is correct, intravenously infused labeled oil which is retained in the lungs should be mixed with and diluted by the fat emboli originating from the blood. Radioactive olive oil of known specific activity was slowly administered to a) control rats, b) rats made lipemic by dietary measures, c) severely traumatized rats, and d) traumatized lipemic rats. There was no difference in the specific activity of the oil recovered from the lungs of rats of any group, indicating that no recognizable amount of blood lipids had been added to the experimentally produced emboli.