Sodium butyrate (NaBu) is known to enhance the rate of biosynthesis of recombinant proteins in Chinese hamster ovary cells (CHO). Here we demonstrate that supplementation with NaBu during rapid growth brings about abrupt death of the cells. The death of the cells is due to apoptosis, as assessed by intranucleosomal DNA fragmentation. The promotion of apoptotic death of the cells could be partially blocked by treatment with the well-known antioxidant, N-acetylcysteine (NAC). Strikingly, the NAC treatment enhanced the production of recombinant EPO twofold compared with that of the culture without NAC supplementation. These results showed that NaBu treatment supplemented with NAC not only inhibits apoptosis, but also exerts a synergistic effect on the biosynthesis of recombinant EPO.