The effect of oral administration of Rosmarinus officinalis L. (Lamiaceae) on CCl(4)-induced acute liver injury was investigated. Rats were daily treated with the plant extract at a dose of 200 mg/kg corresponding to 6.04 mg/kg of carnosol as determined by reverse phase high-performance liquid chromatography. The treatment was initiated 1 h after CCl(4) administration and Rosmarinus officinalis fully prevented CCl(4) effect on hepatic lipid peroxidation after 24 h of CCl(4) administration. The increase in bilirubin level and alanine aminotransferase activity in plasma induced by CCl(4) was completely normalized by Rosmarinus officinalis. The treatment also produced a significant recovery of CCl(4)-induced decrease in liver glycogen content. CCl(4) did not modify the activity of liver cytosolic glutathione S-transferase (GST) compared with that of control groups. However, Rosmarinus officinalis increased liver cytosolic GST activity and produced an additional increment in plasma GST activity in rats treated with CCl(4). Histological evaluation showed that Rosmarinus officinalis partially prevented CCl(4)-induced inflammation, necrosis and vacuolation. Rosmarinus officinalis might exert a dual effect on CCl(4)-induced acute liver injury, acting as an antioxidant and improving GST-dependent detoxification systems.