CLU and Azoospermia: In this preliminary study, we measured and compared serum levels of protein disulfide-isomerase A1, protein disulfide-isomerase A3 (PDIA3), mesencephalic astrocyte-derived neurotrophic factor (MANF), glucose regulatory protein 78 (GRP78), clusterin (CLU), calreticulin (CRT), and calnexin (CNX) between male subjects with idiopathic nonobstructive azoospermia and a control group of noninfertile males.