The aim of this investigation was to determine whether PGE2 regulates TNF release in vitro and in vivo following hemorrhage. To study this, C3H/HeN mice were bled to a mean blood pressure (BP) of 35 mm Hg, maintained for 60 minutes, and then resuscitated. For in vitro studies, peritoneal (pMø) and splenic (sMø) macrophages obtained at 2 hours and 24 hours after hemorrhage were stimulated with LPS for 24 or 48 hours with or without ibuprofen (IBU). For in vivo studies, Mø were harvested 24 hours following hemorrhage with and without IBU treatment and stimulated with LPS for 48 hours. The decreased TNF release by pMø but not sMø from hemorrhaged mice was restored by IBU in vitro. IBU treatment in vivo significantly enhanced TNF release by pMø compared with untreated hemorrhaged animals, while TNF release by sMø was only slightly increased. These data indicate a major role of PGE2 in the regulation of TNF release by pMø following hemorrhage. © 1991 by The Williams & Wilkins Co.