To study the transmigration of fluid rapidly infused intravenously, lactated-Ringer's solution was infused at the rate of 90ml/kg/hr for 30 min into generally anesthetized dogs. Four groups were made; group C with no fluid infusion as the control, group F with rapid fluid infusion only, group LF with renal blood vessels ligation and rapid fluid infusion, and group OF with increased pulmonary capillary permeability experimentally induced by oleic acid and rapid fluid infusion. The extravascular lung water volume (ELWV) was measured by the thermal-sodium double indicator dilution method, and the amounts of ascites and urine, and other clinical parameters were monitored before and after fluid infusion. The results show that in the dogs without increased pulmonary capillary permeability excessive fluid is mainly excreted as urine (group F) or transudates into the abdominal cavity (group LF). But in the dogs with increased pulmonary capillary permeability (group OF) excessive fluid easily and rapidly transudated into the pulmonary interstitium, resulting in pulmonary edema.