Twenty-two adult dogs were each given a single, 30-minute injection of 1.5 ml/kg body weight of pure triolein, and their pulmonary, hepatic, renal, and cerebral morphology was observed for 1, 2, 3, 4, 5, 6, 15, 24, and 48 hours; 3,4, and 5 days; 1 and 2 weeks; and 1 month after the injection. A picture of massive capillary occlusion by lipid droplets was followed by rapidly resolvable inflammatory pneumopathy of granulomatous type, leaving a normal lung at the end of the experiment. The cleaning of the capillaries may be attributed to the mechanical action of the blood flow and to the inflammatory reaction with evacuation of necrotic cells via the bronchial route. Transient pulmonary edema is attributed to increased pulmonary arterial pressure. There was no intravacular coagulation. The few pulmonary lesions observed after the triolein injection suggest that the chemical theory of neutral fat hydrolysis by pulmonary lipase and the toxicity of free fatty acids that are released should be reconsidered.