The effects of nicergoline on changes in enzymatic activities induced by hypoxia and post-hypoxic recovery were studied in various brain areas of young-adult and mature Beagle dogs. In different fractions (homogenate in toto, purified mitochondria, crude synaptosomes, SM1 and SM2 synaptic mitochondria) the maximal rate (Vmax) was investigated of the more representative enzymatic activities of: a) glycolysis, b) Krebs' cycle, c) electron transfer chain, d) amino acid and acetylcholine metabolism, e) lysosomal function. The physiopathological conditions caused alterations in different enzymatic activities depending on the area and subfraction investigated. Nicergoline tended to antagonize some of these alterations. Its action was mainly on non-synaptic mitochondria by a "braking" effect on some key enzyme activities of mitochondrial metabolism (i.e. citrate synthase, cytochrome oxidase and glutamate dehydrogenase) which suggests a sparing action in the brain.