OBJECTIVE: To determine the changes in regional renal blood flow during ureteric obstruction and to examine the role of vasoactive mediators in effecting these changes. MATERIALS AND METHODS: Renal blood flow in Sprague-Dawley rats was assessed after periods of ureteric obstruction using a quantitative autoradiographic technique based on Kety's theory of diffusion of an inert tracer (14C-iodoantipyrine). Prostaglandins, thromboxanes and renin-angiotensin were inhibited pharmacologically using diclofenac sodium and enalapril. RESULTS: Baseline blood flow to the outer cortex, inner cortex and medulla was 807, 258 and 105 mL/100 g/min, respectively. There was an increase in outer cortical blood flow after 10 min of ureteric obstruction which became significant at 30 min (P < 0.05). There was a significant decrease in inner cortical and medullary blood flow at 30 min, to 210 and 68 mL/100 g/min, respectively (P < 0.05). Diclofenac sodium abolished the increase in outer cortical blood flow. After 24 h of unilateral ureteric obstruction, outer cortical blood flow decreased to 492 mL/100 g/min; inner cortical blood flow also decreased but to a lesser extent, to 190 mL/100 g/min. Inhibition of prostaglandins, thromboxanes and the renin-angiotensin system reduced the degree of renal vasoconstriction but there was still a significant decrease in outer cortical perfusion despite the presence of these blocking agents. CONCLUSIONS: The control of the renal vasculature involves a complex interplay between a variety of vasoactive mediators. Quantitative autoradiography offers the opportunity to evaluate changes in regional renal perfusion with high resolution and will allow a greater understanding of the pathophysiology of renal diseases.