 Two novel mono-PEGylated derivatives of hGRF(1-29)-NH(2) [human growth hormone-releasing factor, fragment 1-29] have been synthesized by regio-specific conjugation of Lys(12) or Lys(21) to a monomethoxy-PEG(5000) chain (compounds Lys(12)PEG-GRF and Lys(21)PEG-GRF).     ///    "Secondary structure shifts, hydrogen/deuterium exchange kinetics, temperature coefficients of amide protons, and NOE-based molecular models point out that hGRF(1-29)-NH(2), Lys(21)PEG-GRF and Lys(12)PEG-GRF share a remarkably similar pattern of secondary structure. "    ///    The Lys(12)PEG-GRF regioisomer was found to be slightly less active in vitro than both the unmodified peptide and Lys(21)PEG-GRF. 