Human pancreatic GRF analogs which are extremely potent in stimulating the release of pituitary GH in mammals and which have the formula: H-R-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-R.sub.15 -Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-R.sub.27 -Ser-Arg-Gln-Gln-Gly-Glu-Ser-Asn-Gln-Glu-Arg-Gly-Ala-Y wherein R is selected from the D- and L-isomers of Tyr, Phe and His, R.sub.15 is Gly or D-Ala, R.sub.27 is selected from the group consisting of the D- and L-isomers of Ala, Nle, Ile, Leu, Met and Val, and Y signifies the carboxyl moiety of the amino acid residue at the C-terminal and is the radical --COOR.sub.1,--CR.sub.1 O,--CONHNHR.sub.1,--CON(R.sub.1)(R.sub.2) or --CH.sub.2 OR.sub.1, with R.sub.1 and R.sub.2 being lower alkyl or hydrogen, provided that when R is Tyr, R.sub.27 is other than Met. Phe may be substituted for Tyr in the 10-position, and D-Ala may be substituted for Gly in the 28-position. These peptides or biologically active fragments thereof, which will generally extend from the N-terminal to the vicinity of a residue between positions 27 and 32, as well as nontoxic salts of any of the foregoing, may be administered therapeutically to animals, including humans, and may be used diagnostically.