Lobaria pulmonaria, a lichen species, has been used in traditional medicine for the treatment of various diseases. This study was designed to determine the gastroprotective effect of the methanol extract of L. pulmonaria in an indometacin-induced ulcer model in rats. The results showed that gastric lesions were significantly reduced in a dose-dependent manner. Furthermore, the administration of indometacin caused a significant decrease in the levels of superoxide, glutathione peroxidase and reduced glutathione and an increase in the lipid peroxidation level. Administration of the lichen extract, however, produced an increase in the levels of these enzymes and a decrease in lipid peroxidation levels, although catalase and myeloperoxidase levels were unaffected. The present results suggested that Lobaria pulmonaria has a gastroprotective effect, probably due to reducing oxidative stress and neutrophil infiltration. Copyright (C) 2008 John Wiley & Sons, Ltd.