A new fixed-dose combination drug, Minotensin (1 film-coated tablet contains 120 mg bupranolol, 2.5 mg bendroflumethiazide and 25 mg triamterene) was tested in a long-term study. 20 patients with mild to moderate primary hypertension were treated for 6 months. Items of investigation were: influence on low range serum potassium, influence on serum magnesium concentration, blood pressure lowering effect, tolerance and side effects. Initial dosage of 1 tablet b.i.d. could be reduced to 1 tablet in the morning in 4 patients. The mean serum potassium concentration rose from 3.79 +/- 0.3 mmol/l to 4.15 +/- 0.55 mmol/l (p less than 0.01) after 4 weeks, and to 4.26 +/- 0.37 mmol/l (p less than 0.001) after 6 months of treatment, all single values remaining within normal limits. The serum magnesium concentration rose to a small, insignificant extent. Systolic and diastolic blood pressure were lowered highly significantly from 177 +/- 12/103 +/- 7 mm Hg by 19/11 mm Hg. The mean values were within normal limits (less than 160/95 mm Hg) after treatment. Heart rate fell simultaneously by 11 beats per minute, on average (p less than 0.01). Atrioventricular conduction time was slightly prolonged in 2 cases. Serum levels of sodium, BUN and creatinine rose slightly, but remained within the normal range during treatment. Uric acid and lipids were not influenced significantly. 1 patient complained of transient gastrointestinal discomfort. Generally the drug was tolerated very well.