This study describes and compares the possible effects of vitrification oil the ultrastructural morphology of 20 human mature oocytes vitrified using two different supports, cryoleaf (n = 10) and cryoloop (n = 10). Fresh human mature oocytes (n = 15) were used as controls. Fresh and vitrified-warmed oocytes appeared rounded, with a homogeneous cytoplasm, all intact oolemma and a continuous zona pellucida. Sparse microvacuolization was only occasionally detected in fresh and vitrified-warmed oocytes, to the same extent. About 50% of the vitrified oocytes contained atypical, small and slender mitochondria-smooth endoplasmic reticulum aggregates, whereas a non-homogeneous microvillar pattern wits observable in only 30% of the oocytes subjected to vitrification, regardless of the Support utilized. Cortical granule content appeared generally reduced after vitrification, but cryoleaf-supported oocytes contained more cortical granules than cryoloop-supported oocytes (P