BACKGROUND. Therapy to enhance cholinergic function in the brain is under evaluation for the treatment of Alzheimer's disease. Tetrahydroaminoacridine (tacrine) has recently received a product licence in the United States of America for the treatment of Alzheimer's disease, and the licence application in the United Kingdom will shortly be reviewed. It is therefore possible that this drug will become available for use in the UK in due course. There will then be a need for screening procedures for a large number of elderly patients to decide whether or not they have dementia and, if so, whether it is the result of Alzheimer's disease and is suitable for treatment with the new drug. METHOD. A total of 246 patients aged 75 years or over in two general practices in Bristol were assessed to investigate the potential workload such screening would engender. Three different assessment schedules for the diagnosis of dementia were compared--the mini-mental state examination, the Kew test, and the abbreviated mental test score. RESULTS. None of the assessment schedules was found to be particularly onerous, with median times for administration of five, three and two minutes, respectively. A score of 23 or less on the mini-mental state examination was taken as the main cut-off point for further evaluation. Sixty six patients obtained this score--in 25 the low score reflected factors other than dementia, and 11 others declined further assessment. Of the remaining 30 patients only four had probable Alzheimer's disease at an appropriate level of severity for treatment, and lived with a carer who could ensure compliance and monitor side effects. Two of these patients were receiving conflicting medical treatment and a third declined therapy, leaving only one person for whom treatment could be prescribed. CONCLUSION. It seems likely that of those medically suitable for treatment, it may not be possible to prescribe tacrine for an appreciable proportion. Nevertheless, all potential patients should be screened as the procedures involved are not onerous and at least some of those found suitable for treatment are likely to benefit from this new approach.