Cryopreservation of bovine sperm facilitates the storage and transport of germplasm for use in artificial insemination (AI) and other advanced reproductive technologies. However, cryopreservation can cause irreversible cell damage, thus hindering functionality. Damage occurs to the plasma membrane during the phase transition, and can be reduced by increasing lipid composition, though this alteration also affects the ability of sperm to capacitate and the acrosome to react (Purdy & Graham, 2004a). Treating sperm with cholesterolloaded cyclodextrin (CLC) prior to cryopreservation increases cryosurvival rates (Mocé & Graham, 2006;Purdy & Graham, 2004a) though even with a higher number of viable sperm cells, in vitro embryo production rates and pregnancy rates from AI with control or CLC-treated sperm were not different (Purdy & Graham, 2004b). One potential explanation of this unexpected result is a delay of frozen-thawed CLC-treated sperm to undergo capacitation. Our goal was to investigate the effects of CLC treatment on in vitro capacitation timing.Cholesterol is a hydrophobic molecule that has multiple effects on membranes, including stabilizing the membrane, reducing membrane permeability, influencing the membrane phase transition, serving as a membrane antioxidant, facilitating morphological membrane characteristics, enabling cell-cell interactions, as well as providing suitable microenvironments for membrane-associated proteins (Crockett, 1998). Cholesterol: phospholipid ratio is an