Molecular forms of atrial natriuretic polypeptides circulating in human plasma were analyzed by chromatographic separation, coupled with radioimmunoassay. Analyses were done with human plasma samples taken from 24 human subjects, divided into groups of healthy volunteers, patients with renal disease, and patients with heart disease, with 8 subjects in each group. Although alpha-hANP was found as a major circulating form in most of the plasma specimens (16 cases), beta-hANP accompanied by alpha-hANP was found in 6 cases including 2 healthy volunteers. In addition, hANP-immunoreactive macromolecule, which is likely a bound form of hANP, was found to some extent in all the specimens tested. Diversity of human plasma in ANP molecular distribution was discussed in connection with a radioimmunoassay for plasma ANP.