Neuropeptide Y (a recently discovered brain peptide that is colocalized with norepinephrine within some adrenergic central nervous system neurons) was measured in the cerebrospinal fluid (CSF) from patients with major affective disorder, chronic schizophrenia, and in normal volunteers. No differences between diagnostic groups were found, suggesting that if this neuropeptide is involved in the pathogenesis of these disorders, an abnormality is not detectable in the CSF.