The vitamin B12 (VB12) parameter was studied in the serum and cerebrospinal fluid (CSF) of 14 demented patients. Eleven of these patients were in a state of dementia of the degenerative type such as Alzheimer's disease, senile dementia and Pick's disease. The serum VB12 concentration in all the patients was within normal limits, i.e. 500-1,300 pg/ml. There was no significant difference between the CSF-VB12 levels and the severity of dementia. The serum and CSF-VB12 levels of the demented patients did not show any significant elevation after the oral administration of CH3-B12, 2 mg per day. On the other hand, there was a marked elevation of both the serum and CSF-VB12 after an oral medication (2 mg per day) plus intramuscular administrations (500 micrograms per day). These results confirm that the intramuscular administration of CH3-B12 is an effective way to get a higher value of the serum and CSF-VB12 levels.