Glucose regulated protein 94 (GRP 94) is a resident protein of the endoplasmic reticulum (ER) and is induced by the accumulation of unfolded proteins suggesting that it might associate transiently with a variety of newly synthesized secretory and membrane proteins or permanently with mutant or defective proteins. The highly conserved sequence Lys-Asp-Glu-Leu (KDEL) is present at the C terminus of GRP 94 and other resident ER proteins including GRP 78 and protein disulfide isomerase (PDI). The presence of carboxy terminal KDEL appears to be necessary for retention and appears to be sufficient to reduce the secretion of proteins from the ER. This retention is reported to be mediated by a KDEL receptor. GRP 94 is also a low affinity, high capacity calcium binding protein, though it's role, if any, in calcium regulation is not understood.