considerable evidence from human studies and from investigations of an analogous disease in collie dogs indicate that a regulatory defect at the haematopoietic stem cell level leads to oscillations in production of all typs
es of blood cells. In most patients with cyclic neutropenia, blood neutrophil counts oscillate between mild and severe neutropenia, with counts usually of 0.1 x 109 /L for three to six days with every cycle. It is during these severely neutropenic periods that these patients are particularly predisposed to fever and infection. Characteristically, after the neutropenic period, blood neutrophil counts recover rapidly. Although the other blood cells, including monocytes, eosinophils, lymphocytes, platelets and reticulocytes all ascillate, their oscillations are generally around a mean value which are normal, whereas the mean value for neutrophils is almost always in the moderate to severe neutropenia range.