Exogenous surfactant replacement mixtures currently used for the prevention and treatment of neonatal respiratory distress syndrome are either obtained from mammalian lungs or are totally synthetic. The synthetic surfactants contain no surfactant proteins and tend to show less surface activity than protein-containing mammalian-based surfactants. However, these preparations are more easily prepared and carry less antigenic risk. The next generation of exogenous surfactant promises to be a synthetic lipid mixture that contains recombinant proteins or synthetic peptides. Such mixtures should minimally demonstrate the surface activity and resistance to inhibitory factors displayed by the natural surfactants but have the advantages of synthetic preparations.