1. Dementias have a complex etiology and pathogenesis which should be carefully evaluated in order to attempt a medical treatment. 2. Drugs are among the most frequent causes of dementias, particularly drugs with anticholinergic properties. 3. A similarity between the mental symptoms of anticholinergic poisoning and senile dementia has been observed. 4. Recent investigations have also presented a decrease of cholinergic activity in postmortem material of subjects with Alzheimer's disease. Also a number of data suggest that recent memory would be related to changes in the metabolism of brain acetylcholine (Ach). 5. The possibility that drugs stimulating brain cholinergic mechanisms might be used in the treatment of dementias is envisaged.