Fourteen patients suffering from dementia of the Alzheimer type were treated with tacrine (tetrahydrominoacridine, THA) for 1 year in an open trial. Clinical results were evaluated every third month with neuropsychological tests and rating scales. During the dose-finding, two patients were temporarily withdrawn from medication and one patient was excluded because of elevated levels of liver enzymes. With individualized doses the treatment caused few side effects. Plasma levels of THA varied substantially among patients and correlated with elevation of liver enzymes but not with clinical response. Two patients showed a gradual increase in plasma levels of THA despite unchanged doses. Although results of the neuropsychological tests and clinical ratings were mostly negative, the study indicates that THA can be administered safely for prolonged periods of time. Clinical observations and dose-titration strategy in relation to side effects are discussed.