The effects of the three intravenous anesthetics, ketamine, propofol, and thiopental on superoxide anion production by rat macrophages were examined. Ketamine (30 mu g/mL) significantly inhibited the production of superoxide anion at 30 min after incubation. On the other hand, propofol (50 mu g/mL) significantly inhibited the production of superoxide anion at 15min after incubation. Furthermore, thiopental (200 mu g/mL) markedly inhibited the production of superoxide anion at 15 and 30 min after incubation. However, three intravenous anesthetics at all of concentrations tested failed to significantly modulate the production at 1 to 5 h after incubation. These results suggest that ketamine, propofol, and thiopental may be negative regulators of leukocyte functions.