In summary, ANP exerts its action in the kidney directly and indirectly. Its qualitative importance in body fluid regulation remains unsettled. It appears that its role is more important in pathophysiological conditions such as CHF in which plasma ANP is elevated. Paradoxically, kidneys in heart failure, nephrosis and diabetes are characterized by diminished responsiveness to exogenous ANP. Further studies are needed to ascertain whether this involves an alteration at the receptor or postreceptor site. The cellular mechanisms for receptor regulation and postreceptor signalling in physiology and pathophysiology need further investigation. Finally, a paracrine mode for the action of ANP and other natriuretic peptides has been proposed. Whether they act locally to facilitate sodium excretion and how much importance they have compared to circulating ANP remain to be clarified. The potential role of ANP as a growth inhibitor is also intriguing.