Rosmarinic acid is a naturally-occurring phenolic compound with antioxidant and anti-inflammatory properties. This compound inhibits lipid peroxidation of rat liver microsomes by 90% at a concentration of 25 µg/ml. Rosmarinic acid suppresses endotoxin-induced activation of complement and concomitant formation of prostacyclin. Formation of 5-HETE and LTB4 from human PMNL is inhibited by rosmarinic acid at concentrations of 10-5 to 10-3 M.