The enzymatic activities of two mitochondrial enzymes, i.e. succinate dehydrogenase and NADH-cytochrome c reductase were investigated in the brain of rats at different stages of post-natal development. In addition, the effect of the pharmacological treatment with two drugs, nicergoline and bamethan, able to interact with the alpha or the beta receptors respectively, was evaluated. The results show that both the enzymatic activities rapidly increase in the first days of extra-uterine life, thus indicating an adaptation of mitochondrial oxidative processes to post-natal environmental conditions. The pharmacological treatment with the two drugs does not induce any changes in the enzymatic activities tested.