The formation of disulfide bonds in the endoplasmic reti-culum requires protein disulfide isomerase (PDI) and endoplasmic reticulum oxidoreductin 1 (ERO1) that reoxi-dizes PDI. We report here that the expression of the rat, mouse andhumanhomologues ofERO1-Likeproteinabut not of the isoform ERO1-Lbare stimulated by hypoxia in rats vivo and in rat, mouse and human cell cultures.