Three peptides, B-10148 (Lys-¹-Lys⁰-Arg¹-Pro²-Hyp³-Gly⁴-Igl⁵-Ser⁶-DF5F⁷-Oic⁸; where Hyp is trans-4-hydroxyproline, Igl is α-(2-indanyl)glycine, F5F is 2,3,4,5,6-pentafluorophenylalanine and Oic is (3aS,7aS)-octahydroindole-2-carboxylic acid), B-10206 (DArg⁰-Arg¹-Pro²-Hyp³-Gly⁴-Igl⁵-Ser⁶-DF5F⁷-Nc7G⁸-Arg⁹; where Nc7G is N-cycloheptylglycine) and B-10284 (Arg¹-Pro²-Pro³-Gly⁴-Phe⁵-Thr⁶-DTic⁷-Oic⁸-NH₂; where Tic is 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid), were studied in detail by NMR spectroscopy in 60% CD₃OH/40% H₂O and modeled by a simulated annealing protocol to determine their solution structure. B-10148, an extremely potent BK B₁ receptor antagonist with very high BK B₂ receptor antagonist activity, despite lacking a C-terminal Arg, displayed an ideal type II β-turn from Pro² to Igl⁵, as well as a salt bridge between the guanidino group of Arg¹ and the carboxylate group of Oic⁸. B-10206, the most potent B₂ antagonist, also displayed an ideal type II β-turn from Pro² to Igl⁵ but secondary structure was not observed at the C-terminal end. The third peptide, B-10284, a des-Arg⁹ analog with a C-terminal amide and a very potent B₂ antagonist, had no definite solution structure. The high activity of these peptides emphasizes the importance of the N-terminal β-turn and the hydrophobic character at the C-terminus in determining the activity of bradykinin antagonists.