We have detected retrograde flow by Doppler ultrasound within the hemodialysis access of 10 patients during routine dialysis. Nine of these accesses were prosthetic grafts, and 1 was an autogenous fistula. All 9 of the grafts had access pathology demonstrated by angiography. The single patient with the fistula exhibiting reversed access flow had a poorly developed access with no focal stenoses on angiogram, but 18% recirculation by ultrasound dilution. All patients with retrograde flow had access flow rates below 650 mL/min. While 3 of these patients had substantial access recirculation (2 grafts, 12% and 40%; and 1 fistula, 18%) 2 of these patients had 3% recirculation (2 needle urea method), and 4 patients had 0% access recirculation (ultrasound dilution and 2 needle urea method). We report that retrograde access flow during dialysis may be a specific indicator of access dysfunction. These findings further suggest that retrograde access flow develops before access recirculation, indicating that this finding is more sensitive than recirculation for detecting access dysfunction. Further study is needed to determine the utility of this finding in access surveillance.