In general, dilated and varicose veins are not used as arterial bypass grafts despite their physiological endothelial lining. A uniform small diameter may be achieved by inserting such veins into mesh tubes. To test the degree to which dilated veins can be constricted without forming folds, in-vitro and experimental investigations were performed before such composites were used for clinical reconstructive surgery. Ovine jugular veins with a diameter of 15 mm were inserted into 6 mm tubes. After casting in paraffin wax none of the specimens showed folds on the flow surface. In 12 sheep pairs of mesh-constricted jugular veins and native femoral veins were implanted as femoropopliteal bypass grafts. Six animals were killed at 6 months and 6 at one year. All bypasses remained patent and none showed signs of obstruction caused by folds or anastomotic hyperplasia at angiographic control. Intimal hyperplasia was significantly reduced from 416 +/- 143 microns in the midportion of native vein grafts to 231 +/- 76 microns (p = 0.0001 paired t-test) in constricted veins as well as at the anastomoses (358 +/- 256 microns vs. 180 +/- 73 microns; p = 0.008). Partially or totally mesh-tube-constricted varicose veins were used for infrainguinal reconstructions in 19 patients and for coronary revascularization in 3. All grafts showed an even calibration at control angiography. As constriction does not lead to internal folds, varicose or dilated veins may be used successfully as bypass grafts after insertion into mesh tubes. The external reinforcement reduces the intimal hyperplasia within the graft and also reduces anastomotic hyperplasia.