The effects of Tween 80, a surface active agent which is frequently used for dispersion of water-insoluble subtances, on endothelial function in rabbit aorta were investigated in a cascade superfusion bioassay system by using a deendothelized precontracted rat aorta ring as a bioassay tissue. Prior incubation of rabbit thoracic aorta segments with higher concentrations of Tween XD, caused total inhibition of acetylcholine-induced endothelium derived relaxing factor (EDRF) release, while moderate concentrations had no significant effect. Perfusion of the donor aortae segments with 10(-1)-10(-3) ml/l Tween 80 also inhibited the EDRF release from donor aorta dose-dependently. Histopathological examination of the vasculary wall and endothelial structures revealed a significant desquamation of vasculary endothelium with the highest concentration of Tween 80 used in this study. These data suggest that the mechanism underlying the reduction in the release of EDRF from donor aorta segments may be the destruction by Tween 80 of endothelial lining.