A 67-old man was referred to our hospital because of dyspnea on exertion and severe hypoxia. He had been given, tegafur and OK 432 for seven years following an operation for gastric cancer. Pulmonary hypertension was noted by right heart catheterization. The findings of a transbronchial lung biopsy resulted in a diagnosis of pulmonary veno-occlusive disease. Pulmonary hemodynamic studies were performed for five different agents: nifedipine, beroprast sodium (PGI2), nitroglycerin, theophylline, and isosorbide dinitrate. However, none of these agents showed significant effects on pulmonary arterial pressure or pulmonary vascular resistance. Treatment with glucocorticoid relieved the patient's symptoms without any apparent effect on pulmonary hemodynamics. The long-term administration of anticancerous agents (tegafur) were thought to have caused pulmonary veno-occlusive disease to develop in this patient.