Acute transient hypertension following kidney trauma occurred in a 17-year-old youth due to increased activity of the renin/angiotensin system. The systemic blood pressure and plasma renin activity was also studied following elective kidney resection. In one group of patients the operation was performed with clamping of the renal vessels; in the other no clamping was performed. Only minimal changes in blood pressure and plasma renin activity was found in both groups.