Levels of several antioxidants and related markers were measured in cerebrospinal fluid (CSF) and plasma of 10 Alzheimer's disease (AD) patients and 10 controls. Daily dosage of vitamin C was significantly correlated with both plasma (R=0.662; p=0.0015) and CSF level (R=0.639, p=0.0024). Plasma and CSF vitamin C levels were also highly correlated R=0.793, p<0.0001). Similarly, daily dosage of Vitamin E was significantly correlated with plasma vitamin E (R=0.681; p=0.0009) and showed a trend toward correlation with CSF vitamin E (R=0.422, p=0.06). There were no significant differences between groups in absolute CSF or plasma levels of any analyte. However, the CSF: plasma ratio of vitamin C was significantly greater in the AD patients compared to the controls (p=0.048). In a subset of AD patients, hippocampal volume was significantly correlated with plasma (R2=0.833; p=0.004) and CSF (R2 =0.603; p=0.04) vitamin C levels, and inversely correlated with CSF:plasma vitamin C ratio (R2 =0.717; p=0.016). We conclude that oral vitamin C supplements are delivered to the brain, and speculate that the increased CSF: plasma ratio of vitamin C in AD reflects increased antioxidant consumption by the AD brain.