It has been reported that lithium salt compounds influence hematopoiesis, which is known to be regulated by a number of cytokines, including tumor necrosis factor (TNF), interleukin-1 (IL-1) and interleukin-6 (IL-6). Since lithium can induce TNF production in human monocytes, we wished to determine if lithium carbonate treatment of neutropenic patients affected by breast cancer results in increased cytokine production. Serum levels of TNF alpha, IL-1 and IL-6 were measured before and at 7 and 180 days after treatment with lithium carbonate. Results indicate that this therapy produced TNF alpha and IL-6, but not IL-1 alpha, elevations in patients affected by unmetastasized breast cancer. Conversely, TNF alpha, but not IL-6, elevations were detected in metastatic patients. Studies are under way to investigate the mechanisms by which lithium salts affect cytokine production in monocytes from cancer patients.