We demonstrated that nerve growth factor (NGF) levels were increased in hippocampus and cortical areas, as well as in cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD). Such increases may, at least in part, be due to a decreased expression of the NGF high affinity receptor trkA. Measurement of CSF levels of NGF may add to the repertoire of potential biochemical diagnostic markers in living AD patients.