A two-site ELISA and a bioassay were used to detect NGF-like activity in human brain tissue. Both assays detected mouse NGF and recombinant human NGF with approximately equal sensitivity, whereas the antibodies showed little cross-reactivity with the recombinant human proteins NT-3 and brain-derived neurotrophic factor. NGF-like activity was detected in fresh human cortical samples obtained from epileptic patients, with the highest activity observed in the right hemisphere of men. NGF-like activity was subsequently measured in autopsy samples of frontal and occipital cortex from patients with Alzheimer's disease (AD) and from individuals with no history or pathological evidence of AD. Based on both the ELISA and the bioassay measurements, NGF-like activity was significantly elevated in both brain regions in AD. These results demonstrate the feasibility of detecting NGF-like activity in both fresh and postmortem human brain tissue and further suggest that AD is characterized by increased, rather than decreased, levels of cortical beta-NGF. The AD-related increase in NGF may be a consequence of degenerative changes in the basal forebrain cholinergic system.