Apolipoprotein E (Apo E), one of the major structural and functional apolipoproteins, has recently been implicated in the pathogenesis of Alzheimer's disease (AD). Several studies revealed that Apo E4 isoform is associated with the pathogenic process in AD. A significant reduction of cerebrospinal fluid (CSF) Apo E level in AD patients has been reported in two studies. To further investigate the physiopathological significance of such a variation of Apo E concentration in the CSF, we performed a quantification of Apo E by an enzyme linked immunosorbent assay (ELISA). There were no significant differences in CSF Apo E level between AD cases and control subjects or patients suffering from other neurological diseases. Gender, age and Apo E phenotype explained none of CSF Apo E concentration variability.