SR/CR macrophage killing of S180 cells partially depends upon the production of ROS by the phagocyte oxidase complex. The role of the oxidative burst in purified SR/CR macrophages was elucidated by inhibiting the production and release of ROS and analyzing the effect on in vitro killing of S180 cells. (A) Macrophages were pre-incubated in DMEM without glucose or with 2.8 µM DPI to prevent an oxidative burst. Alternatively, scavengers of O₂^- or H₂O₂ (0.2 mg/ml SOD, 2000 U/ml catalase or 8 mg/ml TG) were used to inhibit the release of ROS. Macrophages were incubated with each inhibitor at least 1 h prior to challenge with S180 cells in vitro. Killing assays were then performed in the presence of the inhibitors at standard conditions as described previously. Results were compared to killing by uninhibited SR/CR macrophages. (B) Macrophages were pre-incubated with thioglycolate at 2, 5 and 8 mg/ml, followed by culture with S180 cells in standard in vitro killing conditions. Results are reported as the mean and standard deviation of S180 cell killing relative to that by uninhibited controls for at least 2 separate experiments. The statistical significance of inhibition of killing as compared to uninhibited control samples was determined by the Student’s t-test. Statistically significant values were defined as P less than or equal to 0.05, and are denoted by a *.