1. In 13 patients with hypertension and renal artery stenosis the stenosis was dilated by an intra-arterial balloon catheter under local anaesthesia.
2. In all but one instance arteriography after the dilatation showed considerable widening of the stenosed area.
3. Six patients had a temporary increase of serum creatinine that lasted only a few days.
4. In seven patients, who had a prolonged transit time at renography, this marker of renal blood flow improved after the dilatation.
5. The effect of the dilatation on the blood pressure in this group of patients, selected on arteriographic criteria only, was variable, but comparable with results of renovascular surgery.
6. Dilatation of renal artery stenosis by an intra-arterial balloon catheter is a promising treatment for patients with hypertension and renal artery stenosis. It is a rapid procedure needing only local anaesthesia. Complications in our experience so far are minor.