A non-invasive method to determine the quantity of pleural effusion and to evaluate the beneficial effect of pleuracentesis in patients with acute exacerbation of chronic congestive heart failure was evaluated. Twenty-three patients with pleural effusion due to acute exacerbation of chronic congestive heart failure were studied. The angle (x) formed by the diaphragm and lung (right side) or pericardium (left side) was measured by ultrasonography in the sitting position using the subscapular approach. Pleuracentesis was then performed in 15 patients, and the quantity of aspirated pleural effusion (y) was measured and compared with the angle x. There was significant relationship between y and x: y = 0.125 x 10(0.017x) (r = 0.77, p < 0.01). The 18 patients with more than 500 ml of estimated one-sided pleural effusion were divided into two groups; the nonpleuracentesis group (n = 8) and the pleuracentesis group (n = 10). The intravenous furosemide dose per increased body weight, and the term of oxygen supply and time to disappearance of edema were compared between the two groups. Intravenous furosemide dose was lower (p < 0.05) and the term of oxygen supply was shorter in the pleuracentesis group than in the nonpleuracentesis group (p < 0.05), whereas time to disappearance of edema was not significantly different. This non-invasive method can estimate the quantity of pleural effusion, and pleuracentesis had beneficial effect on patients with pleural effusion of greater than 500 ml (the angle x > 35 degrees ) in patients with acute exacerbation of chronic congestive heart failure.