1. Differential renal function tests and renography were carried out during infusions of trimetaphan camsylate (Arfonad, Roche) in twenty-three patients with renovascular hypertension resulting from unilateral obstructive disease of the main renal artery. Renal plasma flow, glomerular filtration rate, urinary volume and sodium excretion were measured. Peak-time and slope index were assessed on renograms. Ten patients underwent revascularization of the kidney; nephrectomy was done in thirteen.
2. Patients were divided into two groups according to the response of the contralateral kidney during trimetaphan infusion. Patients in whom vasodilatation occurred were cured both by revascularization and by nephrectomy, whereas no patient who failed to show vasodilatation was benefited by nephrectomy.
3. Renal plasma flow measured under basal conditions was not a reliable index of the anatomical condition of the contralateral kidney, whereas its modification during trimetaphan infusion provided an accurate means of predicting surgical results.
4. When renal plasma flow of the contralateral kidney decreases during trimetaphan infusion, revascularization is still advisable, but nephrectomy fails to correct hypertension.