A method of assisting a mammal having a lung disorder to breathe ambient gas normally, i.e., without the assistance of a ventilator. The method includes providing an animal having a lung disorder, such as surfactant deficiency, stiff lung, or hyperinflated lung syndrome, and instilling a minimum effective dose of a perfluorochemical liquid or emulsion through the trachea for coating the alveolar sacs of a lung of the mammal. The preferred perfluorochemicals have a very low vapor pressure to avoid inducing hyperinflated lung syndrome and are supplied in a minimum effective dosage sufficient to coat the inner lung surfaces. The perfluorochemicals are permeable to the ambient gas and reside substantially permanently within the alveolar sacs without inducing hyperinflated lung syndrome. The liquid is instilled in an amount sufficient to enable the animal to breathe the ambient gas normally with O.sub.2 /CO.sub.2 blood gas exchange. Effective coating of the lungs with a small (generally