The theory shows that access flow can be measured by the dilution technique by reversal of the blood dialysis lines with the venous outlet facing the access stream: (1.) with one dilution sensor in arterial line and two injections Equation (6); (2.) with two matched dilution sensors on the venous line and on the arterial line and one injection Equation (8); (3.) with blood sampling as for recirculation measurement using BUN or other methods in Equation (12). In all cases, accurate measurement of hemodialysis blood flow is required. The results of this bench validation demonstrate that dialysis blood flows, in the clinical range of 200 to 350 ml/min or more, create good mixing conditions in a vascular access model. Accurate measurements are provided for all clinically significant ranges of access flows, needle positions, and vascular access inner diameters. This simple, non-invasive, and inexpensive technique shows great promise for routine diagnosis of vascular access failure in hemodialysis patients.