1) Protein-free plasma extracts from rabbits made anemic by the administration of phenylhydrazine immediately following total body x-irradiation are capable of stimulating erythropoiesis in the normal rat as demonstrated by erythrocytosis, reticulocytosis, and increased marrow erythropoietic activity.

2) Plasma extracts from rabbits made anemic by total body x-irradiation alone contain an erythropoietic stimulating factor.

3) These data would indicate that the stimulating factor is not produced by hemopoietic or other radiosensitive tissue and its formation is not dependent upon a regenerative marrow.

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