Whole-lung lavage under hyperbaric oxygen conditions was performed in two patients suffering from severe respiratory insufficiency in pulmonary alveolar proteinosis. Under these conditions, gas exchange was maintained and the mixed venous partial pressure of oxygen and oxygen saturation showed increases to acceptable levels. This enabled us to limit the FIO2 in order to extend the oxygen tolerance and to perform lavage procedures more effectively. Both patients showed a very significant improvement of their clinical course, and we conclude that elective use of hyperbaric oxygen in unilateral lung lavages should be considered in these severe cases.