The haemodynamic response to oxygen breathing and various vasodilatory drugs (Nifedipine, Ketanserin, Dihydralazine, Nitroglycerin, Iso-Mack, Nit-Ret) was repeatedly measured at different time intervals (4-24 months) in 10 males with hypoxic pulmonary hypertension due to chronic obstructive lung disease. It was found that the pulmonary artery mean pressure and pulmonary vascular resistance changes are stable in most of the patients, discordant reactions being exceptional and of small degree. The authors consider these findings important in the therapeutical decision making for longterm oxygen therapy and or vasodilatory drug administration.