1. Fifty-four hypertensive, hyperuricaemic patients were pair-matched for age, sex and current therapy (diuretic, uric acid-lowering drug).
2. One member of each pair was randomly assigned to continue on the previous therapy and the other member to treatment with tienilic acid (ticrynafen). Routine potassium chloride supplements were given only to subjects who were or had previously been on uric acid-lowering drugs.
3. Blood pressure control was equally good in the tienilic acid-treated and control groups. Serum uric acid was significantly lower in patients treated with tienilic acid.
4. In patients (32) not given supplements of potassium chloride, mean serum K+ did not fall but in four patients (three on tienilic acid, one on cyclopenthiazide) serum K+ fell to 3·5 mmol/l or less and potassium chloride was added.
5. Liver-function tests changed from pretrial results in nine patients. In eight of these (four on tienilic acid and four in the control group) minor rises in alkaline phosphatase only occurred. In the ninth patient, who was also taking metoprolol, serum aspartate transaminase rose markedly after 2 months and fluctuated for 4 months. Eventually there were also rises in alkaline phosphatase and bilirubin; these reverted to normal after stopping tienilic acid.