Three pulmonary surfactant preparations: from human amniotic fluid, from bronchoalveolar lavage fluid, and from cattle lung tissue homogenate were tested in preclinical studies. The preparations are nontoxic, possess no mutagenic, teratogenic, and allergic activities and do not modify visceral morphology after repeated injections. After a single intratracheal administration the drugs normalize arterial blood oxygenation in 15-30 min and arrest the respiratory distress syndrome in dogs, which is confirmed roentgenologically and clinically.