One-pot treatment of N-trityl-L-glutamic acid with DCC followed by DCC-HOBt provided a high yielding synthesis of the 1-hydroxybenzotriazolyl ester of N-trityl-L-pyroglutamic acid (Trt-Glp). Coupling of this active ester with the methyl esters of N-im-tritylated L- and D-histidine provided the corresponding dipeptides which upon saponification and coupling with the methyl esters of L-proline and trans-4-hydroxy-L-proline (Hyp) gave the protected tripeptides Trt-Glp-L and D-His-(N-im- Trt)-Pro-OMe and Trt-Glp-L and D-His(N-im-Trt)-Hyp-OMe. Some 10% of the epimeric (at the His residue) products were formed during this procedure. Sequential saponification and one-pot Mitsunobu-type intramolecular esterification of the latter tripeptides, followed by transesterification with MeOH, provided the corresponding tripeptides Trt-Glp-L and D-His(N-im-Trt)-cHyp-OMe with inversion of configuration at C-4 of the Hyp ring. The observed conformer ratios about the His-Pro amide for all of these tripeptides are discussed in terms of structural features. Detritylation with trifluoroacetic acid followed by ammonolysis completed the synthesis of TRH and its analogues Glp-D-His-Pro-NH2,Glp-L- and D-His-Hyp-NH2 and Glp-L- and -D-His-cHyp-NH2.