The present study was conducted to determine the effects of cumulus cells and sodium pyruvate during in vitro maturation of bovine oocytes on maturation, fertilization, and subsequent development. Cumulus-enclosed oocytes (CEOs) and cumulus-denuded oocytes (CDOs) were cultured for 24 h in polyvinylpyrrolidone-Hepes-tissue culture medium 199 with or without sodium pyruvate. Oocytes were fertilized in vitro and then cultured in CR1aa for 10 days. Before in vitro fertilization, the glutathione (GSH) content of some oocytes was measured. Maturation and normal fertilization rates of CDOs cultured with sodium pyruvate and CEOs were higher than that of CDOs cultured without sodium pyruvate. The CEOs showed significantly higher rates of development to the blastocyst stage than CDOs. The GSH contents of oocytes significantly decreased in CDOs after maturation culture, but the GSH contents of oocytes in CEOs remained at the same level as oocytes before culture. These results indicate that sodium pyruvate promotes nuclear maturation of bovine CDOs and that a continuing presence of cumulus cells during maturation is important for subsequent development of zygotes to the blastocyst stage. However, blastocysts produced from CDOs in the presence of sodium pyruvate showed a developmental competence to be normal calves, but it is not known if CDOs cultured without sodium pyruvate also were capable of developing into calves.