Calf vessel continuity with an intact pedal arch is an important factor in femorodistal (FD) bypass for critical ischaemia. Pulse generated runoff (PGR) was used in combination with the pedal arch patency test of Roedersheimer to determine preoperatively calf vessel and pedal arch patency. Three pedal arch groups were identified; complete (two calf vessels in continuity), incomplete (one vessel) and occluded (no vessels). One hundred non-reversed FD grafts were performed for critical ischaemia (63 men and 37 women), median age 72 (range 43-89 years). Sixteen grafts were to the above knee popliteal artery, 36 to the distal popliteal, three to the tibioperoneal trunk and 45 to a single calf vessel. There were 25 complete, 64 incomplete and 11 occluded pedal arches. The overall primary patency rate was 73%, nine grafts were successfully revised giving a secondary patency rate of 83.5%. The secondary graft patency rates for the above knee popliteal, below knee popliteal, tibioperoneal and single calf vessel grafts were 100, 92, 66 and 66% respectively. The 1 year graft patency rates for grafts to a complete, incomplete and occluded pedal arch were 88, 75 and 9% respectively (Lee-Desu p < 0.01). Similar results were obtained for limb salvage; 100, 84 and 24% respectively (p < 0.01). These results confirm the value of PGR in the preoperative assessment of patients with critical ischaemia. In reconstructions to the popliteal artery, PGR derived pedal arch status does not appear to influence the outcome. By contrast PGR derived pedal arch status in an excellent predictor of success following reconstructions to a single calf vessel.(ABSTRACT TRUNCATED AT 250 WORDS)