The effect of several antifoaming agents by inhalation in preventing paroxysmal pulmonary edema was tested in a series of rabbits. Three single agents (silicone aerosol, freon, and ethyl alcohol vapor) proved beneficial; their combination did not enhance the beneficial effect. A new agent (silicone aerosol) and a new combination (10 per cent ether in alcohol by aerosol) are now ready for clinical trial.