The visible luminescence emitted in the autoxidation of brain homogenates is only partially quenched when antioxidants are added at concentrations such that further oxidation is prevented. From the time course of the emission after antioxidant addition, it can be estimated that nearly 50% of the light arises from an intermediate that decays with a first order kinetics and with a lifetime of ca. 40 s at 32 degrees C. The remaining light arises from the decomposition of one or several intermediates, and show a kinetics that is independent of the incubation time. From the data obtained it is concluded that bimolecular free radical processes, such as the recombination of peroxy radicals, do not significantly contribute to the observed luminescence.