Fursultiamine (TTFD), a derivative of thiamine, at an oral dose of 100 mg/day had a mild beneficial effect in patients with Alzheimer's disease in a 12-week open trial. The improvement could be observed not only in their emotional or other mental symptoms but also in intellectual function. Only mildly impaired subjects showed cognitive improvement. Alzheimer patients' blood levels of thiamine before the trial were within the normal range. No adverse reactions were observed and all patients tolerated the trial well. TTFD could afford an alternate treatment to large doses of thiamine hydrochloride in Alzheimer patients. However, further investigations of the therapeutic implications of thiamine and its possible etiologic clues to Alzheimer's disease are necessary.