The predictive values of blood-flow monitoring using the Doppler effect during operation, to detect anatomical causes of correctable low blood flow or early thrombosis in the absence of correction, was studied in 309 cases of revascularization. When employed under precise conditions, this technique was found to be of high predictive value. Flow rates can be classified in four risk zones: very high, high, low, or nil. In practice, whenever values fall below a critical threshold of 130 ml/min at the iliofemoral level or 55 ml/min at the femoropopliteal level, arteriography should be conducted to establish the cause of the reduced flow, and to enable immediate correction of any technical fault, or improvement in distal flow. The value of this method is shown by the fact that of 44 cases with reduced flow, 22 could not be improved, and early thrombosis occurred in 70% while, in 20 cases, improvement was obtained, and early thrombosis occurred in only 10%. The use of blood-flow monitoring techniques during operation can be assumed to have reduced the incidence of early thrombosis by 27% in those cases with diminished flow, and by 4% in the overall group.