The present invention relates to synthetic lung surfactant compositions that include a novel surface active peptide and a phospholipid, including phospholipase-resistant phospho-glycerol derivatives, phospholipase-resistant phospho-choline derivatives, naturally occurring phospholipids, or a combination thereof. Uses of the surfactant compositions of the present invention to treat endogenous surfactant dysfunctional or deficient lung tissue and to deliver therapeutic agents are also disclosed.