Intermediates play a relevant role in the protein-folding process, because the onset of diseases of genetic nature is usually coupled with protein misfolding and the formation of stable intermediate species. This article describes and briefly discusses the mechanisms considered responsible, at molecular level, for a number of neurodegenerative diseases. In particular, interest is focused on the newly discovered role of cytochrome c in programmed cell death (apoptosis), consisting of acquisition of powerful cardiolipin-specific peroxidase action. Cardiolipin oxidation induces cytochrome c detachment from the mitochondrial membrane and favors the accumulation of products releasing proapoptotic factors. Cytochrome c showing peroxidase activity has non-native structure, and shows enhanced access of the heme catalytic site to small molecules, such as H(2)O(2). The strict correlation linking cytochrome c with the onset of neurodegenerative disorders is described and the therapeutic approach discussed.