We directly measured the net pulmonary extraction of circulating norepinephrine, epinephrine and dopamine in control patients and patients with primary or secondary pulmonary hypertension. Mixed pulmonary artery norepinephrine, epinephrine and dopamine were 314 ± 13 pg/ml, 102 ± 9 pg/mI, 51 ± 5 pg/mi, respectively, for the control group; values were similar in patients with pulmonary hypertension. The pulmonary extraction of norepinephrine was 25.4 ± 2.6% (clearance 266 ± 62 ng/min) in control patients; epinephrine and dopamine were not extracted. There was no net extraction or production of any of the three catecholamines by the lungs in any of the patients with pulmonary hypertension. We conclude that the lungs play a significant role in the inactivation of circulating norepinephrine in man. This metabolic function of the lungs appears to be lost in pulmonary hypertension.