COX1 is the predominant isoforms functional during infectious peritonitis. Selective COX inhibitors (SC-560 for COX1 and NS-398 for COX2) and nonselective COX inhibitors (aspirin and indomethacin) were dosed orally to WT animals 1 hour before GBS injection. Cell-free peritoneal exudate levels of (A) PGE₂ and (B) PGD₂ were measured 3 hours after GBS with similar results obtained for (C) PGE₂ and (D) PGD₂ using COX1 knockout mice. In addition, COX inhibitors were dosed to mice 1 hour before intraperitoneal zymosan (noninfectious stimulus) with cell-free peritoneal exudate levels of (E) PGE₂ and (F) PGD₂ measured 3 hours later. NS-398 was used at dosing levels that do not inhibit (G) COX1-derived plasma TxB₂ measured 3 hours after intraperitoneal GBS injection. Data were analyzed by one-way ANOVA and Dunnett multiple comparison test or by unpaired Student t test. Values are expressed as the mean ± SEM of between 5-12 mice/group. * P < .05; ** P < .01 and *** P < .001.