The present authors conducted a series of experiments with mongrel dogs, in which unilateral chronic pyelonephritis was induced and postoperative changes in blood pressure and plasma renin activity were observed over a period of 3 months. The pyelonephritis infection was brought about by a method involving vesicoureteral reflux and ureteral dysfunction, as described in a previous paper. Pre- and postoperative levels of systolic pressure were compared, but no definite trends were found for the first 3 weeks after operation. At 30, 60 and 90 days the pressures were found to have risen by 21.2 ± 14.6 and 17.1 ± 16.7 mm Hg, respectively. No appreciable change in the plasma renin activity was found, however, at any stage. From these results it was concluded that experimentally induced chronic pyelonephritis in dogs caused a rise in blood pressure. No connection between the pyelonephritis and the renin angiotensin system was found.