Submitochondrial particles from bovine heart in which NADH dehydrogenase is reduced by either addition of NADH and rotenone or by reversed electron transfer generate 0.9 +/- 0.1 nmol of O2-/min per mg of protein at pH 7.4 and at 30 degrees C. When NADH is used as substrate, rotenone, antimycin and cyanide increase O2- production. In NADH- and antimycin-supplemented submitochondrial particles, rotenone has a biphasic effect: it increases O2- production at the NADH dehydrogenase and it inhibits O2- production at the ubiquinone-cytochrome b site. The generation of O2- by the rotenone, the uncoupler carbonyl cyanide rho-trifluoromethoxyphenylhydrazone and oligomycin at concentrations similar to those required to inhibit energy-dependent succinate-NAD reductase. Cyanide did not affect O2- generation at the NADH dehydrogenase, but inhibited O2- production at the ubiquinone-cytochrome b site. Production of O2- at the NADH dehydrogenase is about 50% of the O2- generation but the ubiquinone-cytochrome b area at pH 7.4. Additivity of the two mitochondrial sites of O2- generation was observed over the pH range from 7.0 to 8.8. AN O2- -dependent autocatalytic process that requires NADH, submitochondrial particles and adrenaline is described.