Laser Doppler flowmetry (LDF) was used to evaluate skin post-ischaemic reactive hyperaemia. Four groups of subjects were examined: healthy young and elderly controls (groups A and B) and patients with intermittent claudication or critical ischaemia (groups C and D). The occlusion tourniquet was placed just proximal to the patella, and measurements were performed on the toe pulp (study 1) and leg skin (study 2). The hyperaemic response on both pulp and leg skin was delayed, diminished and prolonged in claudicators compared with controls. On the toe pulp most patients with critical ischaemia had no hyperaemic response at all, indicating that the local vasodilatory capacity was exhausted at rest. The time from tourniquet deflation to pulp peak hyperaemia was the parameter that most clearly separated between the groups [Group A: 21.5 secs (median), group B: 17 secs, group C: 73 secs and group D: greater than 300 secs]. The time from tourniquet deflation to the first increase in flux is probably dependent on hemodynamic factors in the large extremity vessels, and it is possible that this parameter could be used to define levels of hemodynamic significant stenosis in patients with lower limb atherosclerosis. The results also indicate that laser Doppler flowmetry performed during stress testing may be of value in determining appropriate amputation levels.