Cytosolic and mitochondrial alterations induced by exposure of rat astroglial primary cultures to reactive oxygen species (ROS) generated by a xanthine/xanthine oxidase (X/XO) mixture or by lipopolysaccharide (LPS) have been investigated biochemically and immunochemically. In the presence of ROS generated by X/XO, a significant decrease in Cu,Zn superoxide dismutase (Cu,Zn-SOD) and in glutamine synthetase (GS) activity was observed whereas mitochondrial Mn-SOD activity and enzyme protein levels were significantly enhanced. Similar effects on GS, Cu,Zn- and Mn-SOD activities were observed by glucose/glucose oxidase treatment of the cells. Addition of LPS to the cell growth medium also specifically induces Mn-SOD synthesis but was without effect on Cu,Zn-SOD. It is suggested that in all these tested situations, hydrogen peroxide could represent a specific inducer of the observed phenomenon and it may therefore be considered as an intracellular messenger involved in the regulation of some aspects of astroglial oxidative metabolism, particularly the defence against ROS.