We investigated the effects of infusion of somatostatin (200 and 500 ng/kg/min) on central hemodynamics and renal blood flow measured with radioactive microspheres. At the lower dose infusion rate somatostatin did not alter any hemodynamic parameter, but at 500 ng/kg/min somatostatin caused minor transient bradycardia, lowered cardiac output, and increased peripheral resistance. Both infusions inhibited renal arterial flow, with decreases noted in both cortical and medullary components. The 20% fall in renal perfusion was confirmed by the hippurate clearance technique, and there was a corresponding 17% decrease in the glomerular filtration rate. In contrast, no changes were noted in urine output, urinary concentrations of sodium or potassium, or urine osmolarity. These hemodynamic and renal side effects might limit the therapeutic usefulness of somatostatin infusion.