Synthetic pulmonary surfactant

A polypeptide of the formula ##STR3## wherein A.sub.1, A.sub.4, A.sub.5, A.sub.8, A.sub.9, A.sub.11, A.sub.12, A.sub.15, A.sub.16, A.sub.18, A.sub.19 and A.sub.20 are each independently selected from Gln, Glu, Asp, His, Arg, Lys, Ser, Ala, Gly, Tyr, Typ, and Thr;

• A.sub.2 is Leu, Gln, Glu, Asp, His, Arg, Lys, Ser, Ala, Gly, Thr, Typ or Thr;
• A.sub.3 is Pro, Ile, Val, Phe, Met, Ala, Gly, Tyr, Typ or Thr;
• A.sub.6, A.sub.7, A.sub.13 and A.sub.14 are each independently selected from Leu, Ile, Val, Phe, Met, Gln, Glu, Asp, His, Arg, Lys, Ser, Ala, Gly, Tyr, Typ and Thr;
• A.sub.10, A.sub.17 and A.sub.21 are each independently selected from Leu, Ile, Val, Phe, Met, Gln, Glu, Asp, His, Arg, Lys, Ser, Ala, Gly, Tyr, Typ, and Thr;
• T.sub.n is
• T.sub.N '-Arg-Gly-Pro-Pro-,
• T.sub.N '-Gly-Pro-Pro-,
• T.sub.N '-Pro-Pro-,
• T.sub.N '-Pro-, or
• T.sub.N '-;
• T.sub.C is
• -Leu-Gln-Thr-Arg-Gly-T.sub.C ',
• -Leu-Gln-Thr-Arg-T.sub.C ',
• -Leu-Gln-Thr-T.sub.C ',
• -Leu-Gln-T.sub.C ',
• -Leu-T.sub.C ', or
• -T.sub.C ';
• T.sub.N ' is hydrogen, an amino acid, dipeptide, or tripeptide, or an aliphatic, aromatic or cyclic organic acid having 1 to 10 carbon atoms;
• and
• T.sub.C ' is hydrogen, a (C.sub.1 -C.sub.6) alkyl, or benzyl, optionally substituted with one or two members of the group consisting of nitro, methyl and methoxy, or T.sub.C ' phenacyl, phthalimidomethyl, benzhydryl, trichloroethyl, 4-picolyl, .beta.-methylthioethyl or 4(methylthio)phenyl or a pharmaceutically acceptable salt thereof.