Fourteen patients with probable Alzheimer''s disease (AD) participated in an open tetrahydroaminoacridine (THA) treatment trial. Before initiation of THA treatment, a brief battery of neuropsychological tests was performed by an experienced neuropsychologist. The tests were repeated 120 min after a single dose of 50 mg THA had been administered perorally. Thereafter, the patients had a 4-week active treatment with THA 100 mg/day. After the treatment period, eight patients were defined as responders (increase of Mini-Mental State Examination score ≧ 3) and six patients as nonresponders to the treatment. The responders showed significant improvement on Digit Span, Trail Making B, and on both Clock Setting and Clock Recognition tests after 50 mg of THA. The results suggest that in this subgroup of AD patients augmentation of the brain cholinergic systems mainly led to improvement of attentional and frontal-lobe rather than mnemonic functions.