GRP94, also known as Heat shock protein 90kDa beta, member 1 (HSP90B1), is an abundant resident endoplasmic reticulum (ER) lumenal stress protein which together with cytosolic Hsp90 belongs to the Hsp90 family of molecular chaperones. It plays an important role in maintaining protein homeostasis in the secretory pathway. Also, GRP94 can function in the intracellular trafficking of peptides from the extracellular space to the MHC class I antigen processing pathway of antigen presentation cells.