Abstract: Synthetic peptides containing the following specific sequence:Xaa-Pro-Val-Xbb-Xcc-Lys-Arg-W (wherein Xaa is absent or represents Cys or Ser, Xbb represents His or Asn, Xcc represents Leu or Ile and W represents a hydrophobic peptide portion.), an intermediate for producing the peptide, a process for producing the peptide, a lung surfactant comprising the peptide and a lipid mixture and a remedy for respiratory distress syndrome containing the surfactant as the active ingredient. The peptide is easy to isolate and purify and suitable for mass production. As it is highly soluble in methanol and the like, it can readily be blended with a lipid mixture and is suited for the preparation of a lung surfactant. As the lung surfactant has a good supensibility and a potent surface activity, it is useful as a remedy for respiratory distress syndrome.