Somatostatin levels were measured in cerebrospinal fluid of patients with Alzheimer's disease, multi-infarct dementia and normal pressure hydrocephalus and compared with levels from a normal control group. All pathological groups showed a statistically significant decrease of somatostatin with respect to the control group, but no significant differences were found amongst them. A negative correlation was found between the Mini Mental State Test and the somatostatin levels in Alzheimer's disease patients but not in the other groups. Our results confirm that the lower levels of somatostatin in cerebrospinal fluid are not specific to Alzheimer's disease and indicate that the decrease found in all the groups is probably the result of neuronal destruction or damage in the diseases examined.