['Free radicals are reported to be associated with fibrosis in the pancreas. It is generally accepted that pancreatic stellate cells (PSC) play an important role in pancreatic fibrosis. However, the exact role of free radicals in activation of PSC has not been fully elucidated. In the present study, using a superoxide dismutase (SOD) inhibitor, diethyldithiocarbamate (DDC) with cultured PSC, we investigated how free radicals act on the activation of PSC.', 'PSC were isolated from male Wister rats. Cultured rat PSC were incubated with DDC for 48 h. Intracellular SOD activity and lipid peroxidation were examined in DDC-treated PSC. Activation of PSC was examined by determining the expression of alpha-smooth muscle actin (alpha-SMA) by immunocytochemistry. The number of PSC using a hemocytometer, type I collagen secretion with ELISA and matrix metalloproteinases (MMP) activities with gelatin zymography were also examined. Secretion of transforming growth factor-beta1 (TGF-beta1) was evaluated by ELISA. The effects of the allopurinol, a xanthine oxidase (XOD) inhibitor, on PSC were also examined.', 'DDC decreased SOD activity and increased lipid peroxidation products in PSC. DDC activated PSC, increasing the number of alpha-SMA positive cells, enhancing secretion of type I collagen and MMP, inhibiting PSC proliferation. Secretion of TGF-beta1, which is known to activate PSC, was increased by DDC treatment. These alterations were prevented by allopurinol.'] Do xanthine oxidase-derived free radicals directly activate rat pancreatic stellate cells?