Background Control of renal hemodynamics by the arterial baroreflex has never been proved in humans. Apart from the physiological viewpoint, this issue is relevant because altered baroreflex function has been implicated in the pathogenesis of human hypertension.Methods and Results Renal function studies were performed in seated healthy volunteers (n=12; age range, 20 to 34 years) during sustained neck suction at -60 mm Hg, aiming to selectively activate the carotid sinus arterial baroreceptors. Two protocols were followed. One group of 6 volunteers taking a 20 mmol/d sodium diet underwent 90 minutes of neck suction. Compared with a time-control study, neck suction decreased arterial pressure and heart rate; increased glomerular filtration rate (inulin clearance) from 104+-6 to 114+-8 mL/min (P<.01), renal plasma flow (para-aminohippurate clearance) from 616+-52 to 665+-42 mL/min (P<.01), and renal blood flow (from 1120+-95 to 1209+-77 mL/min, P<.01); and decreased renal vascular resistance (from 86+-8 to 76+-6 mm Hg x min x L sup -1, P<.01). Neck suction had no effect on plasma renin activity, aldosterone, atrial natriuretic peptide, catecholamines, and renal sodium excretion. The other 6 volunteers took a normal sodium diet and underwent sustained neck suction for 60 minutes. In this group, no effects on renal hemodynamics could be discerned, despite a modest decrease in blood pressure and heart rate.Conclusions These data show, for the first time, that the arterial baroreflex is involved in the control of renal hemodynamics in humans. However, basal arterial baroreflex control of renal hemodynamics is probably low, and arterial baroreflex activation with subsequent renal vasorelaxation may be found only in conditions in which basal arterial baroreflex control of kidney function is significant, as is presumably the case in seated sodium-restricted subjects. (Circulation. 1994;90: 1883-1890.)