Since no generally-accepted non-invasive test is available for quantification of advanced distal ischaemia of the lower limb, the reproducibility of Laser Doppler flowmetry, skin perfusion pressure and transcutaneous oxygen tension measurement was assessed in 21 patients with severe occlusive arterial disease. The mean coefficients of variation for these methods were 0.11, 0.12 and 0.19 respectively over a 15-minute period without detachment of the measuring devices, and 0.30, 0.29 and 0.37 respectively from day-to-day. However, if tcpO 2 values below 10 mmHg were excluded the corresponding coefficients of variation for this method were 0.08 and 0.31. Thus interventional changes may be detected during continuous monitoring with a reasonable degree of accuracy, but single values can hardly be expected to predict the outcome for the foot in a prospective series, nor can they be used in therapeutic trials of drug action. Major changes in peripheral circulation, for example the effect of revascularisation procedures, can be evaluated using any of the methods studied.