Improvement of the ability to maintain germinal vesicle stage oocytes in vitro is important for the acquisition of developmental competence. Maintaining oocytes at this stage without damaging their quality would allow synchronization of maturation and homogenization of the oocytes population. More investigations are needed to better understand how the oocyte cell cycle is blocked without consequences to future developmental competence. This study tested the efficacy of pharmacological inhibitors of the G2/M cell cycle transition in keeping porcine oocytes at the germinal vesicle (GV) stage and the reversibility of this inhibition. Porcine cumulus-oocyte complexes (COCs) were thus incubated without any hormones for 24 h in the presence or absence of tested inhibitors: 6-DMAP (protein kinase inhibitor, 2 mM), cycloheximide (protein synthesis inhibitor, 2 microg/ml), roscovitine (cyclin-dependent kinase inhibitor, 50 microM) and butyrolactone I (cyclin-dependent kinase inhibitor, 50 microM). Cumulus-oocyte complexes cultured with any of the inhibitors were significantly blocked at the GV stage. The inhibitory effect varied according to the products, with cycloheximide being the most efficient. Reversibility of the pharmacological inhibitors was assessed by culturing COCs an additional 24 h in inhibitor-free culture medium. Examination of oocytes revealed that the inhibitory effect was fully reversible. This study suggests that 6-DMAP, cycloheximide, roscovitine and butyrolactone I can be use to block meiotic resumption in porcine oocytes in NCSU culture medium.