While the effects of reserpine on hypertension in systemic circulation is well known, there have been a few papers on pulmonary circulation. In this paper pulmonary artery pressure response and changes in respiratory functions caused by the administration of reserpine in patients with pulmonic and cardiac disease were studied. Materials and Methods Twenty-seven male and 8 female patients, from 1 1 to 67 years old, were investigated. They were divided into following groups. Thirteen patients with chronic pulmonary disease (3 patients with bronchial asthma, S with chronic pulmonary emphysema, 2 with bronchiectasis, 2 with pulmonary fibrosis, and one with chronic bronchitis). Ten patients with acquired heart disease (4 patients with mitral stenosis, 3 with mitral steno-insufficiency, one with aortic stenosis, and one with aortic insufficiency). Ten patients with congenital heart disease (3 patients with VSD, 3 with ASD, and 4 with pulmonic stenosis), and 2 patients with essenti-al hypertension. Right heart catheterization was performed in the usual manner, then 1 to 2 mg reserpine was injected intramuscularly. Pulmonary circulatory and respiratory functions were observed before and 90 minutes after reserpine injection. In particular, pulmonary artery mean pressure, wedge pressure, and brachial artery pressure were measured at 30, 60, and 90 minutes after reserpine administration. Results I. Respiratory Function. 1) Heart rate (HR) and minute ventilation (VE/M²) After reserpine injection, there were no significant changes in HR and VE/M² in most of the patients. 2) Arterial oxygen saturation (SaO₂) After reserpine injection, SaO₂ decreased on an average of 6 per cent in patients with chronic pulmonary disease, 3 per cent in patients with acquired heart disease, 1 per cent in patients with congenital heart disease and 5 per cent in patients with essential hypertension.