Study of the pulmonary surfactant system has brought important information about its composition, metabolism and functions in the last decades. Besides phospholipids an important role is played by surfactant proteins (SP-A, B, C, D). These proteins aid not only the reduction of the surface tension of the alveoli, but they are involved in regulation of surfactant synthesis, secretion and in local immune defense in the lungs. Impairment of surfactant was found not only in premature newborns (IRDS), but also in cases of meconium aspiration, pneumonia and in other lung diseases in adults. Therapy by stimulation of surfactant synthesis and secretion and by intrapulmonary application of exogenous surfactant was proved effective in therapy of surfactant-deficiencies.