To the Editor: Drs. Morley and Stohlman (N.E.J.M. March 19, 1970) induced bone-marrow depression in dogs with cyclophosphamide (Cytoxan) and produced cyclic neutropenia, which they convincingly ascribed to a deficiency of stem cells. They apparently overlooked earlier observations (Brodsky, Reimann and Dennis, Amer J Med 38:802, 1965) that anticipate their conclusions: here, the downward phase of cyclic neutropenia in man was modified with testosterone injections, and the pyrogen stimulation test of Fink and Calabresi (Ann Intern Med 157:11, 1961) was used to assay marrow stem-cell activity. Marrow granulocytic reserve, found absent at the low phase of cyclic neutropenia, was restored ….