Nineteen patients with senile brain disease (including 2 with parkinsonian symptoms) were treated with amantadine in an oral dosage of 200--300 mg daily. Seven showed definite clinical benefits such as increased alertness and decreased agitation, and 2 others showed slight benefits. However, in only one instance was the benefit maintained without complications. Toxic effects such as overactivity, anxiety and visual hallucinations were observed in 8 patients. Withdrawal effects (e.g., lethargy and staggering) occurred when amantadine was discontinued. The electroencephalograms (EEGs) of all 19 patients showed a frequency increase, chiefly of occipital alpha activity, and sometimes a return to normal, irrespective of clinical changes. Toxic side effects were associated with particularly prominent EEG acceleration. In 10 of the 19 patients, the clinical changes were further validated by by additional psychologic assessments. Although the value of amantadine is limited when given in this way to patients with senile brain disease, it seems important to observe its effects in drug combinations aimed at correction of neurotransmitter imbalances.