Various methods have been used to remove reactive oxygen species (ROS) generated from in vitro culture (IVC) conditions that can cause cell injury or death, including the application of low oxygen (O(2)) tension and the addition of antioxidants. The beneficial effects of antioxidants and O(2) tension on IVC of porcine embryos, however, are controversial among researchers. In this study, we sought to determine the effects and optimal concentrations of antioxidants for the development of porcine embryos in an IVC system. Specifically, we examined the synergistic effects of antioxidants on development to the blastocyst stage in a culture system supplemented with L-cysteine during IVM. Of the antioxidants tested (melatonin, glutathione (GSH), β-mercaptoethanol (β-ME), N-acetylcysteine (NAC) and dithiothreitol (DTT)), addition of GSH (1 mM) or β-ME (25 µM) significantly increased development to the blastocyst stage compared with the controls without antioxidant treatment (22.2 ± 4.2% for 1 mM GSH, 25.9 ± 2.2% for 25 µM β-ME and 12-13% for the control, P<0.05). In addition, the mean cell number per blastocyst was increased by approximately 1.7-fold in the presence of GSH or β -ME. These GSH- and β-ME-induced increases in development to the blastocyst stage and total cell number, however, were not mimicked by melatonin, NAC or DTT, all of which are ROS scavengers. The combination of GSH or β-ME with L-cysteine significantly reduced high O(2) tension-induced ROS production (P<0.05). These results suggest that a combination of 1 mM GSH or 25 µM β-ME with 1 mM L-cysteine could be used for production of high quality porcine blastocysts in IVC systems.