We determined the efficacy of continuous arteriovenous hemofiltration (CAVH) in removing tumor necrosis factor (TNF), thromboxane A2, and prostacyclin, and in improving survival in endotoxemia. Twelve rats were given 10 mg/kg of E. coli 0:127:B8 lipopolysaccharide. Fifteen min later, the rats were randomized to ultrafiltered or non-ultrafiltered groups. Blood and ultrafiltrate were collected for TNF, thromboxane B2 (TxB2), and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). After 4 hr, surviving rats were sacrificed. Five of 6 ultrafiltered and none of 6 non-ultrafiltered rats survived 4 hr. Plasma TxB2 > 1,000 pcg/ml and its rate of increase within the first 2 hr predicted death (P < 0.03). Ultrafiltration decreased the rate of rise in TxB2 (P < 0.04). Plasma TxB2 inversely correlated with TxB2 clearance by ultrafiltration. The concentration and rate of increase in TNF and 6-keto-PGF1 alpha did not predict survival. We conclude that CAVH improves short term survival in endotoxemia. Salutary effects appear to be due to thromboxane A2 removal.