In vitro maturation (IVM) of immature oocytes is an important reproductive technology that generates mature oocytes that are capable of supporting preimplantation embryo development and full development to turm. The developmental competence of oocytes after in vitro fertilization (IVF) was supported in cumulus-cell density dependent manner. The developmental competence of oocytes matured under low oxygen (5% O(2)) tension was higher than that of oocytes matured under high oxygen tensinon (20% O(2)) due to the decrease of reactive oxygen content in the oocyte. To expand the availability of female gamete, an attempt to culture the growing oocytes have been made. We have focused attention on the mitochondrial activity of in vitro grown (IVG) oocytes and shown that L-Carnitine, which acts as a carrier of fatty acids across the inner mitochondrial membrane for subsequent beta-oxidation, supported the viability of growing oocytes. Nowadays, IVM is gaining acceptance in assisted reproductive technology in cattle and human.