Evaluation of cerebrospinal fluid (CSF) via lumbar puncture affords a minimally invasive window into the biochemical substrate enveloping the brain. Multiple previous studies of AD patients compared with control subjects have demonstrated decreased CSF beta-amyloid, and elevated CSF tau protein. Previous longitudinal studies have documented the stability of CSF beta-amyloid over one year and CSF tau over two years in AD, suggesting that these may be possible stable target measures for therapeutic intervention.