Addition of glucose to activated RAW 264.7 macrophages or addition of mitochondrial electron-transfer chain inhibitors enhanced the cellular nitric oxide production. An additive effect of rotenone or antimycin A and glucose on enhancing nitric oxide production was shown. Uncoupling the mitochondria by a chemical uncoupler decreased nitric oxide production. The mitochondria membrane potential was found to be important for cell viability. Although nitric oxide is the physiological inhibitor of mitochondrial respiration, this study indicates that mitochondria were not inhibited in the activated macrophages. Furthermore, a role of mitochondria in the rapid regulation of nitric oxide synthesis by the inducible nitric oxide synthase has been demonstrated.