Atrial natriuretic peptide (ANP), a peptide released from the cardiac atria, compensates blood volume expansion by its diuretic, natriuretic and vasoactive properties. We measured human plasma ANP(hANP) levels in patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and progressive systemic sclerosis (PSS) and found that their values were higher than those of healthy controls. In SLE patients, hANP levels correlated with serum creatinine concentration and the patients with proteinuria showed high levels of hANP. Administration of large amount of corticosteroid as a remission induction of the patients with SLE caused high levels of hANP. In patients with PSS, %FEV1 showed strong inverse correlations between hANP levels, and the patients with an enlarged second curvature of the heart had high levels of hANP. In patients with RA, no significant correlation was found between hANP levels and clinical variables including patients' age.