The conformational properties of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and various analogs and homologs were studied by circular dichroism (CD) spectroscopy in solvent mixtures inducing secondary structures. The CD spectra obtained for rat ANF(99-126), porcine BNP32, and their related analogs indicated that these peptides exhibited mainly a random-coil conformation in pure water. However, the addition of increasing concentrations of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) gave rise for all peptides to a more ordered secondary structure. The analysis of the far-ultraviolet CD spectra suggested that the peptides exist under two conformational states, beta-turn and beta-sheet, in the presence of 20-60% HFIP/water solutions. Moreover, the characterizations of rANF(99-126) and the analog pBNP1, which combines the cyclic core of bBNP32 with the carboxy- and amino-terminal segments of rANF-(99-126), have been carried out by Fourier transform infrared spectroscopy (FTIR) in 40% HFIP/D2O. The FTIR results indicated that these peptides exist predominantly under a beta-turn and beta-sheet mixed conformation. In addition, the amount of organized secondary structure obtained for human BNP32, bovine aldosterone secretion inhibitory factor, also known as ASIF(69-103) and beta-rANF(92-126), in the presence of a 40% HFIP/phosphate buffer mixture, was similar to that of porcine BNP32, whereas rat BNP32 was found to be more structured. In the same solvent mixture, the CD spectra of Met(O)110-human ANF(99-126) and chicken ANF(99-126) indicated that these peptides possess conformational features different to those of rANF(99-126) and hANF(99-126). Porcine CNP22, C-type natriuretic peptide, and the fragment C-ANF exhibited undefined secondary structure in the presence of 40% HFIP/phosphate buffer. These results suggest that the amino acid residues, not common to the various natriuretic peptides, would be involved in the stabilization of either beta-turn and/or beta-sheet conformations. Moreover, these secondary structures appear as particularly important for the recognition of the ANF-R1A receptor subtype found in bovine adrenal cortex.