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Measurements were made to characterize the relationship between erythropoietin output and erythropoiesis in two groups of subjects, one moved from a sea level habitat to high altitude, and the second moved from a high altitude habitat to sea level. In the first group, there was a latent period of 6 hours followed by a rapid increase in erythropoietin, and a secondary fall to a level of approximately twice normal. The increased erythropoietin stimulus was also reflected in a shortened marrow radioiron transit time. In the second group, there was an initial unexplained rise, after which erythropoietin fell within 8 hours to undetectable amounts. Elevated erythropoietin was associated in Group I with an increased iron uptake within 24 hours of the stimulus, suggesting a direct action of erythropoietin on hemoglobin synthesis by the existing marrow population. Limitation in erythropoiesis to a rate of less than twice normal was tentatively explained by a restricted iron supply. In the second group, marrow activity continued for 3 days despite a marked fall in erythropoietin, indicating that cells in the maturation phase completed their normal development.

A study of the processes of formation and destruction of blood has been carried out, in addition to other investigations of the physiopathology of the anemia of human bartonellosis. From the results obtained the following conclusions may be drawn: 1. The life-span of the red cells parasitized by Bartonella bacilliformis is greatly shortened. However, not all the parasitized red cells are prematurely destroyed. 2. Red cells from normal subjects are partially destroyed when they are injected into infected patients. More than 50 per cent of them survive normally. 3. The mechanical fragility of the red cells is increased in the majority of the cases. 4. The index of sequestration of red cells by the liver and spleen was increased in the three patients studied. Also, the products of catabolism of hemoglobin were increased in all the patients studied. 5. The increased production of red cells as a response to the great destruction was prevented at first, but later it reached its peak, being in some cases five times greater than normal. 6. The search for agglutinins and hemolysins was negative. 7. The amount of free protoporphyrins in the red cells was increased, indicating that there was some interference to the synthesis of hemoglobin that would also explain the hypochromia of the red cells. 8. The increase in the diameter of the red cells was independent of the actual amount of reticulocytes.

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