In situ saphenous vein arterial bypass flow was studied in 16 patients with respect to level of epidural anaesthesia. Arterial pressure and electromagnetic flow were used to evaluate arterial tone by intra-arterial (i.a.) papaverine. Eight patients had a low epidural block (< or = Th. 10) and eight patients were operated during high epidural anaesthesia (> Th. 10). Flow increased and arterial pressure decreased after i.a. papaverine in all patients. When compared with patients operated during high epidural anaesthesia, flow increase and decrease in vascular resistance took place in patients operated during low epidural anaesthesia (P < 0.02). Increase in arterial flow after i.a. papaverine was not significantly different in patients operated in low epidural and general anaesthesia (n = 8). In eight patients with insulin-dependent diabetes mellitus who had low epidural anaesthesia, the increase in flow after i.a. papaverine was not significantly different to that noted during high epidural anaesthesia. The results indicate that the level of analgesia influences graft flow after i.a. papaverine, probably reflecting differences in the effect of epidural anaesthesia on sympathetic tone to the leg.