The efficacy of ticrynafen in the treatment of hypertension in patients with moderate renal impairment was compared with that of hydrochlorothiazide in a randomised, double-blind crossover trial in eleven subjects with renal insufficiency. Significant reductions in blood pressure occurred with both treatments, with the maximum responses occurring at different time intervals and to different degrees in individual patients. Thus, although ticrynafen caused a significant reduction in blood pressure in this group of hypertensive patients with renal insufficiency, it was not consistently different from that which could be achieved with hydrochlorothiazide. Ticrynafen also significantly reduced the serum uric acid concentration, compared with a significant rise with hydrochlorothiazide. No major biochemical abnormalities or side-effects were encountered in any subject. Thus, in these patients with renal insufficiency, ticrynafen still demonstrated a uricosuric effect as well as a useful anti-hypertensive action.