The invention provides synthetic peptides which are extremely potent in stimulating the release of pituitary GH in animals, including humans and also resist enzymatic degradation in the body. The peptides have the sequence: (B)R.sub.1 -R.sub.2 -R.sub.3 -Ala-(Q.sub.1)R.sub.5 -Phe-Thr-R.sub.8 -Ser(Q.sub.2)R.sub.10 -Arg-R.sub.12 -(Q.sub.3)R.sub.13 -Leu-R.sub.15 -Gln-(Q.sub.4)Leu-R.sub.18 -(Q.sub.5)Ala-Arg-R.sub.21 -(Q.sub.6)R.sub.22 -(Q.sub.7)Leu-R.sub.24 -R.sub.25 -(Q.sub.8)R.sub.26 -(Q.sub.9)R.sub.27 -R.sub.28 -Arg-Gln-Gln-Gly-Glu-R.sub.34 -Asn-Gln-Glu-R.sub.38 -R.sub.39 -R.sub.40 -Arg-R.sub.42 -R.sub.43 -R.sub.44 wherein R.sub.1 is Tyr, D-Tyr, Met, Phe, D-Phe, pCl-Phe, Leu, His or D-His; B is H, C.sup.a Me, N.sup.a Me, desamino, Ac or For; R.sub.2 is Ala, D-Ala, NMA or D-NMA; R.sub.3 is Asp or D-Asp; R.sub.5 is Ile or Leu; R.sub.8 is Ser, Asn, Lys, Arg, Asp or Glu; R.sub.10 is Tyr, D-Tyr or Phe; R.sub.12 is Arg or Lys; R.sub.13 is Ile, Val, Leu or Ala; R.sub.15 is Gly or Ala; R.sub.18 is Ser or Tyr; R.sub.21 is Lys, D-Lys, Arg or D-Arg; R.sub.22 is Leu, Ile, Ala or Val; R.sub.24 is Gln or His; R.sub.25 is Asp or Glu; R.sub.26 is Ile or Leu; R.sub.27 is Met, D-Met, Ala, Nle, Ile, Leu, Nva or Val; R.sub.28 is Asn or Ser; R.sub.34 is Ser or Arg; R.sub.38 is Arg or Gln; R.sub.39 is Gly or Arg; R.sub.40 is Ala or Ser; R.sub.42 is Phe, Ala or Val; R.sub.43 is Asn or Arg; R.sub.44 is a natural amino acid; Q.sub.1 -Q.sub.9 are either H or C.sup.a Me, provided however that one of Q.sub.1 -Q.sub.9 is C.sup.a Me. These peptides may also be used diagnostically, and the C-terminus can be shortened to residue-29.