Abstract
1. In 20 patients suffering from mild hypertension (WHO classification I-II) the effect on vigilance was studied under double-blind conditions. Ten patients were given guanfacine 2 mg daily and ten others a placebo preparation. 2. Before the study and following 2 weeks' medication a battery of tests was applied in which the reaction time and attention were subjected to comparative analysis. The variation in blood pressure and heart rate under mental stress conditions was also tested. 3. The study shows a non-significant reduction in blood pressure in the guanfacine group without the parameters of vigilance being affected. Under mental stress, there was no impairment of haemodynamic reactions. 4. It is concluded that guanfacine, at the selected dose of 2 mg daily, has no apparent effect on the vigilance of hypertensive patients.