Hospital patients with depressed arterial oxygen tensions (PaO2) from pulmonary disease were given antipyrine orally or intravenously. The half-time (t1/2) of disappearance from plasma was measured. Other patients with normal PaO2 measurements were treated similarly. Patients whose PaO2 was 55 or below had longer t1/2 times than those of patients with a PaO2 above 55. This observation parallels that made previously in rats.