To study hemopexin metabolism the turnover of ¹²⁵I-labeled plasma hemopexin was determined in 10 control subjects, five patients with erythropoietic protoporphyria, one with porphyria cutanea tarda, and two with sickle-cell disease. Hemopexin half-life in the control subjects (mean ± S.D.) was 7.1 ± 1.0 days, and fractional catabolic rates were 23.6 ± 3.0 per cent of the plasma pool per day.

¹²⁵I-hemopexin catabolism was accelerated over controls in each of these illnesses, with fractional catabolic rates of 27.6 ± 2.1 per cent in erythropoietic protoporphyria (p<0.05), 35 per cent in the patient with porphyria cutanea tarda and 41 and 32 per cent in the patients with sickle-cell disease. Since the calculated synthetic rates for hemopexin fell within the normal range in these patients, reduction in plasma hemopexin levels observed was accounted for by accelerated breakdown. Injection of heme into a control subject produced marked acceleration of hemopexin catabolism, providing further documentation for the role of hemopexin in the clearance of plasma heme in man. (N Engl J Med 290:822–826, 1974)