The level of the apo-form of the copper enzyme ceruloplasmin (CP) is an established peripheral marker in diseases associated with copper imbalance. In view of the proposal that disturbances of copper homeostasis may contribute to neurodegeneration associated with Alzheimer's disease (AD), the present work investigates, by Western blot and non-reducing SDS-PAGE followed by activity staining, the features of CP protein, and the copper/CP relationship in cerebrospinal fluid (CSF) and serum of AD patients. Results show that only a fraction of total copper is associated with CP in the CSF, at variance with serum, both in affected and in healthy individuals. Furthermore, a conspicuous amount of apo-ceruloplasmin and a decrease of CP oxidase activity characterize the CSF of the affected individuals, and confirm that an impairment of copper metabolism occurs in their central nervous system. In the CSF of AD patients the decrease of active CP, associated with the increase in the pool of copper not sequestered by this protein, may play a role in the neurodegenerative process.