Extensive proton magnetic resonance experiments were carried out on three bradykinin peptide antagonists B-9430, B-9436, and B-9858 in aqueous solutions as well as in sodium dodecylsulphate micelles (B-9430 and B-9436) and CD 3 OH/H 2 O (60%/40%) mixtures for B-9858. All three peptides showed no observable secondary structure in aqueous solution. However, in their respective structure-inducing solvents, B-9430 (B 1 and B 2 receptor antagonist) and B-9436 (a B 2 receptor antagonist) exhibit a type II b-turn involving residues 2-5, and B-9430 also exhibits a type II b-turn involving residues 6-9 (in sodium dodecylsulfate micellar solutions), whereas B-9858, a B 1 -specific receptor antagonist, exhibits only a type II b-turn involving residues 2-5 (in CD 3 OH/H 2 O solutions). Simulated annealing calculations on B-9858 confirm the experimental conclusions based on the nmr data. In addition, simulated annealing of the (2S, 3aS, 7aS)-octahydroindole-2-carboxylic acid (Oic residue), which is present in two of the three decapeptides studied, show that the one-chair conformation of the six-membered ring predominates, in agreement with the experimental data. The activities of these peptides are compared with their secondary structures and the specific receptor activity appears to depend on the presence of specific amino acid residues, such as N-(2-indanyl)glycine (Nig) and D[ a-(2-indanyl)glycine] (D-Igl) as well as on elements of secondary structure.