The capability of an ethanol extract of Rosmarinus tomentosus to protect rat liver in an experimental model of cirrhosis induced by thioacetamide (TAA) has been evaluated. Four groups of rats were used: Two of them received 300 mg TAA/l in the drinking water for 3 months while the other two, which served as controls, were given water ad libitum. During the same period and for each one of the treatments, one group received a semi-purified (SP) diet and the other one was fed the same diet supplemented with 1% of the dry residue obtained from R. tomentostis ethanol extract (SP + E). There was a significant reduction of TAA toxicity in rats fed the SP + E diet, as assessed by plasma and liver biochemical markers, and by liver histopathology. Plasma total protein concentration was restored, urea concentration and plasma alkaline phosphatase and gamma-glutamyl-transferase activities were reduced. A significant correction of plasma fatty acids concentrations was also evident. Hepatic alkaline phosphatase and gamma-glutamyl-transferase activities were significantly reduced in animals fed SP+E diet and glucose-6-phosphatase activity was significantly enhanced. The results suggest that R. tomentosus ethanol extract administered in the diet affords protection against TAA-induced cirrhosis, preventing most of the histological changes and functionality alterations own to this experimental pathology. (c) 2005 Elsevier GmbH. All rights reserved.