Thirteen patients with atrial septal defect (ASD), 12 ostium secundum type, 1 ostium primum type and left-to-right shunt were studied by M-mode and two-dimensional echocardiography and then by intravenous contrast study. Diagnostic confirmation was obtained in 12 cases by cardiac catheterization and angiocardiography. The purpose of the study was to assess the value of contrast echocardiography in the diagnosis of ASD without pulmonary hypertension, since it is known that the standard echocardiographic investigation is rather unsatisfactory in this type of malformation. M-mode echocardiography with contrast injection has been diagnostic in 12 cases (92.3%), by visualising contrast echos in the mitral tunnel. The overall reliability of the two-dimensional contrast-echocardiography was reduced in our cases by a fairly high number of inaccurate results. The right to left shunting of injected contrast does not seem to depend on the haemodynamic parameters considered, such as right atrial pressure, right ventricular end-diastolic pressure, pulmonary artery pressure, and pulmonary arteriolar resistance.