Three analogs of the atrial natriuretic peptide ANP(105-126), lacking the N-terminal exocyclic peptide segment and containing 2-mercaptoacetic acid, 3-mercaptopropionic acid or 4-mercaptobutyric acid in place of the cysteine residue in position 105 of the peptide sequence, were synthesized by the solid-phase method. The resulting des-amino analogs showed 2 to 4 times higher diuretic/natriuretic activity than the most active natural ANP and displayed a potent hypotensive effect as well. All three analogs were relatively less potent in various in vitro bioassays and in a binding assay, indicating that their high activities in vivo may be due to resistance to enzymatic degradation and to reduced non-specific tissue adsorption. These compounds not only will serve as useful pharmacologic tools but also represent prototypes for the development of further reduced-size ANP analogs.