HVA and 5-HIAA levels in CSF were investigated in ten patients with presenile Alzheimer's dementia. As reported by others, CSF levels of dopamine and serotonin metabolism are lower in patients with presenile dementia than in normal controls of the same age. After lumbar puncture, the patients were treated with cerebral cortex phospholipids (200 mg i.v. daily). This produced a significant increase in CSF levels of HVA and 5-HIAA, as well as a reduction of serum PL. The data are interpreted as proving an active pharmacological action of cerebral cortex phospholipids on the various processes of the neurotransmitter substances in demential syndromes.