The respiratory distress syndrome of the newborn is a disorder in which the pulmonary surfactant is deficient. It has not been possible to completely replace natural components of surfactant with synthetic components and achieve a mixture which functions physiologically like pulmonary surfactant. Therefore, studies of replacement therapy for surfactant deficiency have used complete natural surfactants or derivatives of natural surfactant which contain the defined components of surfactant. The surfactant used in the clinical trial was derived from human amniotic fluid.