Daily levels of urinary colony-stimulating factor (CSF) were measured in two patients with cyclic neutropenia. The CSF levels increased during the neutropenic period concomitant with the maximum peripheral monocytosis. Simultaneous erythropoietin (ESF) levels were measured in one of these patients. ESF also increased in the neutropenic period antecedent to the periodic reticulocytosis. These studies are compatible with a negative feedback system regulating both granulocytopoiesis and erythropoiesis. Whether the cyclic fluctuations of these substances are causally related to the cyclic marrow proliferation is uncertain.
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Guerry et al. (1974) studied this question.