A series of atrial natriuretic peptides, viz., alpha-r-ANF, APII, APIII, and des-Ser5, Ser6-APII, have been obtained by condensation of earlier synthesized fragments promoted with complex F. Acetylaminomethyl protecting group were removed from cystein residues with simultaneous cyclization of the peptide. Biological activity of the atrial natriuretic peptides was studied.