1. Single and multiple injections of CXM (methyl acetamide and p-chloroxylenol) have a similar action in increasing the total number of polymorphonuclear leukocytes in the peripheral blood of a group of 32 rats. No "shift to the left" takes place.
2. There is no stimulation of the myeloid elements of the bone marrow to suggest that this leukocytosis is due to hyperplasia.
3. The evidence suggests that the mechanism for the leukocytosis produced by the CXM consists of releasing blood cells from depots in the body. This action is selective for the granulocytes as the red cells and platelets are not affected.
4. There is progressive degeneration of the parenchymal cells of the liver after single and multiple injections of these substances.
5. If less toxic combinations of methyl acetamide and para-chloro-xylenol could be obtained, they might be of value in the treatment of certain patients with leukopenia or agranulocytosis more particularly when the bone marrow is hyperplastic but the granulocytes are not released.
The author expresses his appreciation to Dr. Oscar Riddle for the generous provision of animal and laboratory facilities.