The identification of a biochemical marker of Alzheimer's disease (AD) is a major research aim of many groups. Abnormal levels of tau and Abeta have been identified in the cerebrospinal fluid (CSF) of AD patients, although the sensitivity and specificity of the changes in these two biomarkers alone is not sufficient to be of diagnostic value. Recently, our group has identified an abnormality in the glycosylation of acetylcholinesterase (AChE). The increase in this glycoform of AChE is very specific for Alzheimer's disease and is not seen in many other neurological diseases including other dementias.