Data obtained from a patient with polycythemia secondary to a patent ductus arteriosus with reverse flow, have been presented. Oxygen saturation and tension of brachial arterial blood and sternal bone marrow were within normal limits, while those of the iliac marrow and femoral arterial blood were reduced.

The presence of polycythemia under such circumstances is thought to exclude a primary cerebral or pituitary mechanism. Similarly, the presence of hypercellularity and normoblastic hyperplasia in normally oxygenated areas of the bone marrow argue against a direct effect of lowered O2 content or pO2 on germinal erythroid cells.

These observations are compatible with a humoral regulation of erythropoiesis in the hypoxic state.

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