Near-infrared spectroscopy was performed perioperatively on the dorsum of the foot in 14 patients who underwent infrainguinal bypass surgery using a prosthesis or the greater saphenous vein. Dual-wavelength continuous light spectroscopy was used to assess changes in tissue saturation before, during and after the operation. Following the use of peripheral vascular grafts an immediate postoperative increase in tissue saturation of median 28 (range -10 to +81) arbitrary units was noted (P <0.01). Following distal clamping of the common femoral artery, maximal ischaemia corresponding to a median reduction in tissue saturation of 61 (range 6-94) units was reached after 26 (range 8-95) min (P <0.01). The maximal tissue saturation following declamping was median 27 (range -16 to +100) units higher than the preoperative level (P <0.01) and was reached after median 42 (range 8-125) min. The results indicate that near-infrared spectroscopy is appropriate for perioperative monitoring during vascular grafting.