The structure and function of short-length amino terminal PTH analogues were studied. The substitution of Leu⁷ with Phe in [Ala³,¹⁰Leu⁷Arg¹¹]rPTH (1-11) NH₂ analogue peptides did not show any reduction in cAMP formation. Replacement of the 1^st, 7^th and 8^th residues revealed different activities, depending upon the residue type. The substitution of Ala¹ by Ser in [Ala³,¹⁰Leu⁷Arg¹¹]rPTH (1-11) NH₂ caused nearly a complete loss of cAMP formation. Meanwhile, NMR analysis of [(Ala¹/Ser¹) Ala³,¹⁰ (Leu⁷/Phe⁷) Arg¹¹]rPTH (1-11) NH₂ revealed an α-helical backbone structure with a flexible conformation at the carboxyl-terminus. The overall results suggest that 11-residue short oligopeptide analogues of PTH tend to form an α-helical structure and the different activities of those analogues could be associated with residue specificity rather than the secondary conformational structure.