Autosomal dominant cyclic hematopoiesis (ADCH), or cyclic neutropenia, is a genetic disorder characterized by cyclic oscillations of neutrophils and other blood cells. To determine if the gene for ADCH mapped within the major hematopoietic regulatory gene cluster at 5q23.3-q33.3, we tested five families with ADCH for genetic linkage between the disorder and loci on chromosome 5q. Two-point analyses gave significant evidence in favor of excluding linkage between ADCH and the hematopoietic genes granulocyte-macrophage colony-stimulating factor (CSF), interleukins 3, 4, 5, and 9, and the receptor of macrophage-CSF. Furthermore, the exclusion data provide evidence for rejecting the hypothesis that ADCH may be encoded by a new gene mapping within this cluster.