The time course of blood pressure reduction after transluminal dilatation of renal artery stenoses was investigated by repeated 24 h blood pressure monitoring in 17 patients with renovascular hypertension. The results of treatment were compared for the different types of stenoses. The diurnal and nocturnal variations in blood pressure were not altered. The mean blood pressure in all patients during daytime (0800-2000) was 160 +/- 13/99 +/- 7 mm Hg (mean +/- SD syst./diast.) before dilatation, 151 +/- 10/91 +/- 6 mm Hg on the day of dilatation (p syst. less than 0.01, p diast. less than 0.01) and 151 +/- 9/91 +/- 6 mm Hg 1-4 weeks after. Blood pressure was further reduced to 137 +/- 12/84 +/- 8 mm Hg after 9-11 months despite a reduction in drug treatment (p syst. less than 0.001, p diast. less than 0.001). After 9-11 months the reduction in blood pressure (0800-2000) was 31/21 mm Hg (mean syst./diast. reduction) in the patients with only one kidney and 29/20 mm Hg in subjects with fibromuscular dysplasia. In the patients with arteriosclerotic renal artery stenoses who had two kidneys the blood pressure was reduced by only 18/11 mm Hg. The results of repeated ambulatory blood pressure monitoring indicate that the initial fall in blood pressure after dilatation of renal artery stenoses is followed by a delayed further reduction. Subjects with only one kidney and patients with fibromuscular dysplasia show the most effective reduction in blood pressure after dilatation of renal artery stenoses.