In a case with Jakob-Creutzfeldt disease, investigations in cerebrospinal fluid and brain tissue showed disturbances of the monoamine metabolism. The levels of the eatecholamines were seriously decreased. Loading tests with probenecid suggested a low dopamine turnover. The lactate-pyruvate ratio in CSF was normal. The histopathological findings are in good agreement with the biochemical data. The investigatio might possibly support the theory of a viral etiology in Jakob-Creutzfeldt disease, and that a virus infection could be responsible for the impairment of the monoamine metabolism.