OBJECTIVE:To determine if the developmental potential of embryos resulting from in vivo- and in vitro-matured monkey oocytes could be increased through the use of a coculture system.DESIGN:Randomized prospective comparison of embryos resulting from either in vitro- or in vivo-matured oocytes cocultured with Vero cells or cultured in medium alone (control).SETTING:Basic research laboratory.MAIN OUTCOME MEASURES:In vitro embryo development to the blastocyst stage and blastocyst hatching.RESULTS:No significant difference in development was noted between coculture and control groups with embryos resulting from in vivo-matured oocytes. However, coculture was found to improve significantly the development of monkey embryos resulting from in vitro-matured oocytes.CONCLUSIONS:These results demonstrate that primate embryos resulting from in vitro-matured and in vitro-fertilized oocytes differ in their culture requirement when compared with embryos resulting from in vivo-matured oocytes.