Application of recombinant DNA technology to the study of atrial natriuretic factor (ANF) has significantly increased our understanding of the biochemistry and physiology of this cardiac hormone. Molecular characterization of the ANF gene and mRNA has yielded structural details about this peptide, and provided tools to investigate maturation, storage, and secretion of a cardiac hormone. Genetic probes have facilitated analyses of the role of a natriuretic and vasorelaxant hormone in pathophysiologic states. Furthermore, studies on the regulation of this cardiac gene have begun to provide data on the molecular basis for biochemical changes in the heart that occur in response to physiologic and pathologic processes.