To verify the existence of ipsilateral reno-renal reflexes we studied the effect of surgical denervation of one kidney on the ipsilateral efferent renal nerve activity (ERNA), in the absence of contralateral afferent renal nerve activity. Thus the ipsilateral renal denervation was performed 1 h later than the contralateral renal denervation. The experiments were done on 9 anesthetized cats. Arterial pressure, urine flow rate (UFR) of both kidneys and ERNA to the ipsilateral kidney were measured. All variables were monitored during a 3 min control period and for 13 min after either contralateral and ipsilateral renal denervations. ERNA significantly increased (+20 +/- 9%) and UFR concomitantly decreased (-11 +/- 10%) after the surgical denervation of the contralateral kidney which showed an increase (+91 +/- 19%) in UFR. The subsequent ipsilateral denervation caused a significant increase in UFR (+117 +/- 25%) and ERNA (79 +/- 23%) of the same kidney, while on the opposite side UFR did not change. During the two procedures, arterial pressure did not change. Our data demonstrate the existence of ipsilateral reno-renal reflexes that exert a tonic inhibitory effect on ipsilateral ERNA.