The effects of coenzyme Q(10) (CoQ(10)) and alpha-tocopherol at the rate of mitochondrial superoxide anion radical (O-2(.-)) geration were examined in skeletal muscle, liver and kidney of 24-day-month mice. Mice were orally administered alpha-tocopherol (200 mg.kg(-1).day(-1)) alone, CoQ(10) (123 mg.kg(-1).day(-1)) alone, or the two together for 13 wk. Administration of alpha-tocopherol resulted in a similar to sevenfold elevation of mitochondrial alpha-tocopherol content. Intake of alpha-tocopherol alone caused an similar to fivefold increase in CoQ content (CoQ(9) and/or CoQ(10)) and alpha-tocopherol of mitochondria. The rate of O-2 generation by sub mitochondrial particles (SMPs) was inversely related to their alpha-tocopherol content but unrelated to CoQ content. Experimental in vitro augmentation of SMPs with varying amounts of alpha-tocopherol caused an up to similar to 50% decrease in the rate of O2T generation. Similar in vitro augmentations of SMPs with CoQ(10) had previously been found to have no effect on O2+ generation The CoQ(10)-induced elevation of alpha-tocopherol in the present study was inferred to be due to a sparing/regeneration by CoQ. results indicate the involvement of alpha-tocopherol in the elimination of mitochondrially generated O2T.-Lass A., Sohal, R. S. Effect of coenzyme Q(10) and alpha-tocopherol content of mitochondria on the production of superoxide anion radicals. .