To determine whether phosphatidylinositol 3-kinase (PI 3-kinase) cascade plays any role in mammalian oocyte meiotic progression, porcine oocytes were matured in vitro with PI 3-kinase specific inhibitors, wortmannin and LY294002. In cumulus-oocyte complexes (COCs), the addition of 10^-8, 10^-7 or 10^-6 M wortmannin or 0.5, 5.0 or 7.5 ×10^-5 M LY294002 to the medium significantly reduced the proportion of oocytes exhibiting germinal vesicle breakdown (GVBD) compared with the inhibitor-free control. In denuded oocytes (DOs), no significant differences in the incidence of GVBD were found between 10^-8 M wortmannin treatment and controls, and between 10^-8 and 10^-7 M treatments, respectively. LY294002 treatment at all concentrations tested did not significantly affect GVBD in DOs. When COCs were cultured in the presence of wortmannin or LY294002, the proportions of oocytes arrested at GVII were significantly higher than the control. The degree of cumulus cell expansion was significantly decreased with wortmannin or LY294002 treatment compared to the control. We concluded that activation of PI 3-kinase in cumulus cells is closely associated with meiotic resumption of the porcine oocytes and the cumulus cell expansion.