Thirty patients with moderate to severe, uncontrolled hypertension were treated with a captopril/frusemide combination. The initial dose of captopril (6.25 mg or 12.5 mg) produced an acute fall in BP from 162 +/- 6/102 +/- 3 to 132 +/- 6/85 +/- 3 mmHg but at a dose of 12.5 mg three times daily outpatient BPs were not controlled. Frusemide (40 mg/day) was added and increased as necessary at two week intervals until BP was satisfactorily controlled or a total daily dose of 160 mg was reached. During long-term follow-up over a mean period of two years good BPs were achieved with an average daily dose of frusemide of 95 mg and captopril 52 mg (148 +/- 3/90 +/- 2 mmHg). There was no overall change in renal function or plasma potassium although small rises in blood urea were seen in some patients. In a group of 28 patients controlled on this regimen a change to a twice daily schedule without alteration of the dose of captopril or frusemide did not affect clinic BPs. In addition, BP remained controlled throughout the day as measured at home with an electronic sphygmomanometer. No case of glucose interolence was observed despite high doses of frusemide (HbA1 = 7.1 +/- 0.12%) and in 12 patients, where prospective measurements of HbA1 were measured, there was a fall from 7.6 +/- 0.21% to 6.9 +/- 0.16% suggesting an effect of captopril on insulin sensitivity. We conclude that low dose captopril with a variable frusemide dosage represents a simple and effective treatment for moderate to severe hypertension.