Measurements of adenosine triphosphate concentration and adenosine triphosphate/diphosphate ratio provided quantitative markers for medial integrity and stimulated (vortex-mixing) prostacyclin production for endothelial function. Freshly isolated vein had an adenosine triphosphate concentration of 470 +/- 60 nmol X gm-1 wet weight and an adenosine triphosphate/diphosphate ratio of 2.50 +/- 0.13; it produced prostacyclin at a rate of 9.3 +/- 1.0 pg X min-1 X mg-1 wet weight. Vein subjected to dissection, proximal anastomosis, and distention with the patient's own arterial pressure had an adenosine triphosphate concentration of 490 +/- 70 nmol X gm-1 wet weight and an adenosine triphosphate/diphosphate ratio of 2.29 +/- 0.13; it produced prostacyclin at a rate of 10.4 +/- 2.2 pg X min-1 X mg-1 wet weight. All values were indistinguishable from those in freshly isolated vein. In vein subjected to dissection, distention at less than 300 mm Hg with patient's heparinized blood, and distal anastomosis, adenosine triphosphate concentration, adenosine triphosphate/diphosphate ratio, and prostacyclin production (5.5 +/- 0.6 pg X min-1 X mg-1 wet weight) were all significantly (p less than 0.001) reduced. These results demonstrated that surgical preparation by first proximal anastomosis preserved both medial and endothelial function.