Cardiac myocytes synthesize and secrete a family of peptide hormones with potent natriuretic, diuretic, and vasodilatory properties. These peptides are derived from precursor molecules that are encoded by two different genes, the atrial natriuretic peptide precursor A (NPPA) and the B-type natriuretic peptide or natriuretic peptide precursor B (NPPB). A human genomic clone for the NPPB gene was used to determine the chromosomal location of the NPPB gene. Analysis of Southern blot hybridization to DNAs from various somatic cell hybrids and fluorescence in situ hybridization allowed assignment of the NPPB locus to human chromosome 1p36. This location coincided with that of the NPPA locus; pulsed-field gel electrophoresis placed NPPA and NPPB within 50 kb of each other. This close chromosomal linkage, together with the conserved primary sequences and structural organization of the two natriuretic peptide precursor genes, suggests that the natriuretic peptide loci may have evolved from a common ancestor gene.