BACKGORUND: Trauma, surgical stress, and anesthesia are often associated with postoperative immune suppression and an increased susceptibility to infection. The role of propofol in a patient who may be at the risk of impaired immune function is contradictory. To access the possible role of propofol on human immune function, we investigated the cytotoxic activity of mononuclear cells from peripheral blood. METHODS: Healthy human mononuclear cells (MNCs) were isolated and stimulated with lipopolysaccharide (LPS) for 5 hrs. Activated MNCs were cultured in the presence of varying concentrations of propofol for 20 hrs and lactate dehydrogenase (LDH) release was measured to evaluate NMC cytotoxicity against K-562 cell target cells (cell to target 40:1). RESULTS: Propofol exposure at concentrations of 1, 5 and 10mug/ml did not significantly affect LDH release from K-562 cells, but the cytotoxic activity of MNCs was significantly suppressed at a concentration of 50mug/ml. (P<0.01) CONCLUSiONS: Since the concentrations of 1, 5 and 10mug/ml of propofol are in the clinically acceptable range for sedation and anesthesia, this result suggest that propofol does not significantly alter the cytotoxicity of NMCs in septic conditions.