Transient granulocytopenia and lymphopenia may occur in acute alcoholics without splenomegaly, cirrhosis, infection, and megaloblastic anemia due to folate deficiency. The bone marrow in granulocytopenic patients is frequently hypocellular with few mature granulocytes, and the functional marrow granulocyte reserve is reduced. These findings suggest a depressed granulopoietic activity in these patients. The mechanism by which alcohol suppresses granulopoiesis remains unclear. Direct toxicity of alcohol on granulopoietic stem cells and increased individual susceptibility to the toxic effect of alcohol may be important factors. Alcohol also causes functional impairment of granulocytes (adherence, motility, and chemotaxis), macrophages (motility and phagocytosis), and lymphocytes (blastogenic transformation and development of delayed dermal hypersensitivity reaction), probably by perturbation of the cell membrane resulting in an increased intracellular cyclic AMP level.