Injection of testosterone, nortestosterone, or oxymetholone markedly enhanced granulopoietic recovery in mice made neutropenic by 1,3-bis(2-chloroethyl)-1-nitrosourea, vinblastine, or cyclophosphamide. Blood neutrophils rose to six times normal counts, and the bone marrow showed sequential increases first in dividing granulocytic elements and later in the nondividing reserve. The steroid-induced increase in myeloblasts was preceded by an increase in in vitro colony-forming cells and colony-forming units. Mice whose spleen colony-forming units had been eradicated by busulfan failed to show a granulopoietic response to androgens. The relationship between colony-forming units and -forming cells is discussed, and it is suggested that the granulopoietic effect of steroids results from stimulation of the proliferation of unipotential, granulocytic, colony-forming stem cells.

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Supported by USPHS Grant CA08736.

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