In this study, the effects of Melissa officinalis L. extract on hyperlipidemic rats were investigated, morphologically and biochemically. The animals were fed a lipogenic diet consisting of 2% cholesterol, 20% sunflower oil and 0.5% cholic acid added to normal chow and were given 3% ethanol for 42 days. The plant extract was given by gavage technique to rats to a dose of 2 g/kg every day for 28, 14 days after experimental animals done hyperlipidemia. The degenerative changes were observed in hyperlipidemic rats, light and electron microscopically. There was a significant increase in the levels of serum cholesterol, total lipid, alanine transaminase (ALT), aspartate transaminase (AST) and alkaline phosphatase (ALP), a significant decrease in the levels of liver tissue glutathione (GSH), a significant increase in the levels of tissue lipid peroxidation (LPO) in this group. On the other hand, the administration of Melissa officinalis L. extract reduced total cholesterol, total lipid, ALT, AST and ALP levels in serum, and LPO levels in liver tissue, moreover increased glutathione levels in the tissue. As a result, it was suggested that Melissa officinalis L. extract exerted an hypolipidemic effect and showed a protective effect on the liver of hyperlipidemic rats. (c) 2005 Elsevier Ireland Ltd. All rights reserved.