A case of periodic neutropenia of twenty years’ duration is presented. ACTH was administered intravenously in an attempt to abort or prevent the neutropenic cycles. No effect in raising the total leukocyte or neutrophil count was noted, and the neutropenic cycles could not be prevented by the ACTH. A striking absence of fever, stomatitis, or other secondary manifestations occurred during the neutropenic periods treated with ACTH. The background for treating such conditions with hormones is discussed.