The authors examined the relationship between patency after thrombectomy of clotted dialysis grafts and intraoperative measurements of flow (Q), pressure gradient (Pgr), and longitudinal resistance (Rl). Eighteen thrombosed arteriovenous (AV) grafts underwent 21 thrombectomies. Pressures at arterial (P1) and venous (P2) ends of the AV grafts were determined with 22-gauge catheters and standard transducers; flow was measured with transit-time probes; arithmetic averaging of waveforms was used to compute mean Q, Pgr, and Rl. Kaplan-Meier patency curves were analyzed by using log rank methods. Mean patency for all grafts was 164 ±152 days. For each variable, the 21 measurements were split and the patency curve for the grafts with the 11 lowest value grafts was compared to the curve representing the 10 highest value grafts. The difference between high Rl versus low Rl patency curves was significant with high-resistance grafts having a median patency of 55 days and low-resistance grafts having a median patency greater than 151 days (p = 0.0089). In contrast, the high Q group median patency was 151 days versus 174 days for the low Q group (p = 0.86). Median patency for the low Pgr group was 115 days compared to 62 days for the high Pgr group (p = 0.162). Longitudinal resistance within AV grafts, but not flow or pressure gradient, showed a significant correlation with patency after thrombectomy. Increased resistance to flow within AV grafts appears to be an important factor affecting the propensity of dialysis grafts to thrombose.