The therapeutic efficacy and tolerance of guanfacine after 5-7 years' continuous treatment was investigated in 54 patients (30 females and 24 males) who were part of the 580 hypertensives originally participating in a 1-year clinical study reported previously. Only 41% of the patients were treated with guanfacine alone (mean daily dose, 2.2 mg), whereas 59% received combined drug therapy (mean daily dose of guanfacine, 5.7 mg). The results on efficacy and dosage after 5-7 years were identical with those obtained for the entire group after 1 year (n = 580) and 2 years (n = 162). The blood pressure of these patients was reduced from pretreatment values of 186/112 +/- 12/11 mmHg to 149/93 +/- 14/19 mmHg at the final examination. Thirty-four of the patients (63%) had normalized blood pressure. Six patients (11%), all of whom had been on combined therapy, complained of dryness of the mouth. Practically no other side effects and no drug interactions were observed, nor were there any signs of pharmacologic resistance.