We evaluated the effects of the substrate and inhibitors related to phosphatidylinositol metabolism on in vitro maturation and fertilization of porcine oocytes. Cumulus-oocyte complexes were cultured in mTLP-PVA medium supplemented with or without inositol (250 mM) fur 46h. Subsequently, these oocytes were inseminated with fresh boar semen in mTALP-PVA medium for 6h. At 6h after insemination, oocytes were cultured for further 12 h in TCM-199 supplemented with 10% FBS (fetal bovine serum). The higher percentage of oocytes in inositol-supplemented medium reached metaphase of the second meiotic division compared to those in control (81.4% vs. 67.3%; P<0.()5). following 18 h of insemination, more number of male pronuclei were formed in the oocytes matured in inositol-supplemented medium than in those of control experiment (42.0% vs. 27.3%; P<0.05). When oocytes were cultured in medium with 10mM LiCl (chloride lithium) or 0.5mM dbcAMP (dibutyryl cyclic adenosine monophosphate) to determine the role of inositol on the maturation of oocytes, these two drugs inhibited the meiotic division of oocytes (P<0.05). However, addition of inositol to the culture medium did overcome the inhibitory effect of these drugs on the oocyte maturation. DbcAMP and verapamil supplemented synergistically arrested the meiotic division of oocytes. Addition of verapamil did not inhibit germinal vesicle breakdown, but it severly inhibited the second meiotic division of oocytes. These results suggest that inositol exert its improving effects on maturation, by activating the PI (phosphatidylinositol) cycle and causing beneficial changes in both cytoplasm and membrane of oocytes.