Background. Endothelial dysfunction can play a key role in early no reflow and late accelerated cardiac graft arteriosclerosis. We studied the direct effect of reduced glutathione (GSH) on the preservation of endothelial function of coronary arteries subjected to prolonged cold storage. Methods. Ring preparations were dissected from rat left coronary arteries and mounted on an isometric wire myograph. After control measurements, artery segments were exposed to 15 hr of hypothermic (+4°C) incubation in either normal saline (group 1), GSH-free Celsior solution (a new heart preservation solution) (group 2), or Celsior solution with 3 mmol/L of GSH (group 3). Results. After storage, the basal tone was increased in groups 1 and 2, but it did not change in group 3. The endothelium-dependent relaxation to acetylcholine was reduced in groups 1 and 2, but it was not affected in group 3. The sensitivity to acetylcholine was decreased in group 1, and there were no changes in groups 2 and 3. Conclusions. Our data suggest that fresh GSH in Celsior solution improves preservation of coronary endothelial function.