Twenty-one patients with partial anomalous pulmonary venous drainage with intact atrial septum have been studied. These include 13 patients not previously reported from our laboratories and eight patients with complete hemodynamics reported by others. Methods for identification of this abnormality and for identification of an intact atrial septum are described, including differential indicator dilution curves, catheter probing of the atrial septum and pulmonary angiography. Blood flow through anomalously draining lobes of the lung is usually higher than through normally drainage lobes attributable to the higher pressure differences across the anomalous lung, right atrial pressure being uniformly lower than left atrial pressure. The pulmonary vascular resistance when "standardized" to the flow of blood normally present in different portions of the lung indicated that no significant differences existed between normally and anomalously draining lobes. Six patients had coexisting rheumatic mitral stenosis and one had congenital mitral stenosis. Its influence on the hemodynamic changes produced by PAPVD is discussed.