Impaired energy metabolism is an early, predominant feature in Alzheimer's disease. In order to find out simple, reliable 'in vivo' markers for the clinical-biological typization of the disorder, we measured cerebrospinal fluid (CSF) glucose, lactate and pyruvate levels in patients suffering from dementia of Alzheimer type (DAT) and in healthy elderly controls. DAT group showed remarkably higher levels of pyruvate (P = 0.01), with no overlap with the values obtained in controls. CSF pyruvate levels were also significantly associated with the severity of dementia. Therefore, CSF pyruvate levels neatly separate DAT patients from controls, having also pathogenetic value.