An analysis of 82 limbs subjected to femoropopliteal bypass grafting demonstrated that electromagnetic flow wave forms of the reconstructed vessel are a reliable indicator in predicting the outcome of surgery. On the basis of this knowledge, postoperative follow-up study of patients who had undergone reconstructive surgery was carried out. Early occult occlusive lesions were detected in 5 of 56 limbs examined, and 3 of these patients underwent successful reoperation with satisfactory restoration of blood flow. Follow-up study using flow wave form analysis is a useful method of detecting occult changes in arteries and leads to early treatment.