Synthetic peptides that differ in their lipid-peptide interactions were combined with dipalmitoylphosphatidylcholine (DPPC) and tested in an adult rat lavaged lung model in vitro for efficacy as totally synthetic lung surfactants. The putative amphipathic alpha-helical region of the major lung surfactant apoprotein (SP-A81-102), an analogue with increased amphipathic alpha-helical potential ([Lys88,97,Glu99,Trp102]-SP-A81-102]), and the hydrophobic peptide gramicidin D were all ineffective. Three water-soluble lipid-binding peptides that contain amphipathic alpha-helical regions were also tested. Of these, only a 24-residue amphipathic alpha-helical peptide (18As) based on the lipid-binding sequences of the plasma apolipoproteins was effective. Melittin and glucagon were ineffective. Mixtures of 18As and DPPC also restored gas exchange in an in vivo lavaged guinea pig lung model to 90-95% of its prelavage value and maintained it for at least 3 h. Mixtures of DPPC and 18As are also surface active (gamma min less than 4 mN/m in the pulsating bubble). These data demonstrate the efficacy of a combination of a single lipid and a small, water-soluble, nonhemolytic, synthetic peptide containing an amphipathic alpha-helical structure and a sequence unrelated to any of the reported lung surfactant apoprotein sequences.