In this study, access flow in hemodialysis patients with bridge grafts was measured by a newly developed device. The technique is based on the measurement of changes in the ultrasound characteristics of blood. These changes were initiated by an injection of isotonic saline and measured in the tubes of the extra-corporeal circuit. The access flow rate (mean +/- standard variation) was 880 +/- 440 mL/min (range, 166 to 1740) (N = 46). The mean coefficient of variation was 13.4 +/- 6.8% (median, 13.0%; range 3.5 to 29.4%). Measurements correlated well (r = 0.91, N = 22, P < 0.001) with flow rates determined by magnetic resonance angiography and by a technique based on intra-access flow-pressure curves (r = 0.84, N = 14, P < 0.001). In conclusion, access flow can be measured easily, noninvasively, and reliably by the ultrasound dilution device.