1. A case of coexistenst chronic lymphatic leukemia and polycythemia vera is described.
2. The source of the erythrocytosis was not apparent. Erythroid hypoplasia was seen in the bone marrow, and there was no apparent extramedullary hematopoiesis in specimens of liver or spleen.
3. Plasma iron contenst was inordinately low, and this was confirmed by a correspondingly high plasma iron-binding capacity. No stainable iron could be demonstrated in the tissues examined.
4. The curve for plasma iron clearance was best satisfied by two components of different negative slopes. The more rapid had a half-time of 0.2 hours and probably represented removal of iron for erythropoiesis. The slower had a half-time of 10.2 and probably represented extrahematopoietic iron utilization.
5. Erythrocyte radioiron utilization was greater than normal and approximated 100 per cent within nine days. This could have been a manifestation of depleted iron stores, accelerated erythropoiesis, or both.