Microglial activation induced by beta-amyloid (A beta) is an important cellular response in the pathogenesis of Alzheimer's disease (AD). In this study, we show that reactive oxygen species (ROS) play a role as signaling molecules for the activation of NF-kappaB and induction of IL-1beta mRNA expression in A beta(25-35)-treated murine microglia BV-2 cells. ROS scavengers such catalase and superoxide dismutase (SOD) mimetics obviously reduced activation of NF-kappaB and the elevated level of IL-1beta transcripts induced by A beta(25-35). In addition, the A beta(25-35)-induced NF-kappaB activation and IL-1beta expression were suppressed by blockers of the ROS generating enzymes such as NADPH oxidase, cyclooxygenase, and lipoxygenase. These data suggest that ROS mediate A beta-induced microglial activation.