Plasma oxidant activity (marker of reactive oxygen metabolites) and the unfractionated leucocyte filterability rate (determined through 5 micron pore diameter Nuclepore filters, using a positive pressure system) were monitored in 15 stage II peripheral vascular disease (PVD) patients before and after ischaemia was induced by treadmill exercise (12 degrees slope/2 km/hour). Plasma oxidant activity increased (+ 115%) significantly (p less than 0.001) at the maximum walking time, correlating (r = 0.79) with a significant (p less than 0.001) impairment (+23%) in the unfractionated leucocyte filterability rate. At the transcutaneous oxygen pressure (tcPO2) half recovery time the plasma oxidant activity approached basal values but the unfractionated leucocyte filterability rate remained significantly (p less than 0.001) impaired (+16%). It returned to basal values at the full tcPO2 recovery time. These results show reactive oxygen metabolites are released during ischaemia of the lower limbs and are correlated with a significant impairment in the flow properties of leucocytes.