This randomized, double-blind, placebo-controlled study evaluated the antipyretic effect and safety of intravenous (i.v.) acetaminophen using an endotoxin-induced fever model. Subjects exhibiting sufficient fever response following administration of reference standard endotoxin (RSE) were randomly assigned to receive i.v. acetaminophen 1,000 mg (n = 31) or matching placebo (n = 29). The primary efficacy end point was the weighted sum of temperature differences from baseline through 6 h. Relative to placebo, i.v. acetaminophen administration produced a rapid decrease in temperature that persisted throughout the 6-h study period. The primary end point favored i.v. acetaminophen over placebo (P < 0.001). Temperature differences from baseline reached statistical significance at T30 min after endotoxin administration (15 min after completing the study medication infusion). Acetaminophen administered i.v. was well tolerated, and the frequency of adverse events was comparable to that after administration of i.v. placebo. This study shows that i.v. acetaminophen in a single 1,000-mg dose is safe and effective in reducing fever.