Propofol and midazolam are the most widely used sedatives in the intensive care setting after surgery. We studied whether these sedatives had any antitumor immunity effects in mice. Mice were given intraperitoneal injections of propofol or midazolam and subcutaneous inoculation of tumor cells (EL4). Then, spleen cells were collected and the in vitro activity of cytotoxic T lymphocytes (CTL) was measured using flow cytometry. The in vitro activity of CTL against EL4 was significantly greater after propofol injection compared with its vehicle (Intralipid) or saline. Midazolam had no effect on CTL activity. We also studied whether tumor growth in vivo was affected by the administration of propofol. Tumor growth was significantly suppressed in mice that were given propofol, compared with tumor growth in mice given saline. Therefore, it is concluded that propofol may have a beneficial effect on antitumor immunity in mice.