Leucocyte-derived free radicals were monitored in 30 stage II peripheral vascular disease (PVD) patients in an open placebo-controlled study. Linked to a transcutaneous oxygen pressure (TcPO2) monitor, they performed two consecutive standard treadmill tests (5 min, 2 km h-1, 12% slope) before and after 15-days treatment with placebo or a leucocyte-derived free radical scavenger (Piroxicam, 20 mg day-1), the second test being carried out at the TcPO2 half-recovery time. Blood samples were collected at baseline, at the maximum walking times and the TcPO2 half recovery times. The total and differential leucocyte counts, the percentage of cells with pseudopodia or cytoplasmatic irregularities, the filterability rates (using a positive pressure Nuclepore filter system) of the main leucocyte subfractions and plasma oxidant activity were monitored. Compared with values before treatment and with the placebo-treated group Piroxicam therapy significantly (P less than 0.001) reduced the final half-recovery time, the percentage of cells with pseudopodia and the level of plasma oxidant activity (P less than 0.01) and kept the granulocyte filterability rate stable, showing leucocyte-derived free radicals are involved in peripheral ischaemia.