Resistance to the natriuretic action of atrial natriuretic peptide (ANP) is a hallmark of states of pathological sodium retention including congestive heart failure, cirrhosis of the liver, and nephrotic syndrome. A variety of mechanisms including reduced delivery of filtrate to ANP-sensitive sites in the inner medullary collecting duct and diminished receptor density in this tubular segment have been offered to account for this resistance. Recent studies in experimental nephrotic syndrome and in liver disease produced by ligation of the common bile duct in rats suggest that increased activity of cyclic guanosine 3',5'-monophosphate (cGMP) phosphodiesterase may be an important mediator of renal resistance to ANP. Such increased enzyme activity rapidly catabolizes the second messenger cGMP, normally formed when ANP interacts with its biologically active natriuretic peptide. A receptors, thereby leading to blunted ANP responsiveness. This increased phosphodiesterase activity offers a novel approach to the management of clinical conditions associated with sodium retention and edema formation.