Using a simple, sensitive model, it has been demonstrated that intravenous administration of high doses of contrast medium can induce pulmonary edema in non-anesthetized rats. The degree of edema formation, which is dependent on the rate of injection as well as dose, is greatest immediately after injection and then decreases slowly. The amount of fluid accumulation in the lungs is related to the chemotoxicity of the medium as other solutions of equivalent hyperosmolality did not induce the same degree of pulmonary edema.