The present invention is related to synthetic and/or recombinant biologically active peptide derivatives of PTH(1-28). Some of the peptides of the invention are at least 90% identical to a peptide consisting essentially of the amino acid sequence X.sub.01ValSerGluIleGlnLeuMetHis AsnLeuGlyLysHisLeuAsnSer MetX.sub.02ArgValGluTrpLeuArgLysLysLeu (SEQ ID NO:1), wherein X.sub.01 is Ser, Ala or Gly; and X.sub.02 is Glu or Arg.