Bovine zygotes derived from oocytes matured and fertilized in vitro were cultured in vitro. In Exp. 1, zygotes were vortexed to remove cumulus cells and then cultured in oviduct epithelial cell-conditioned TCM-199 medium with or without added cumulus cells. Embryos cultured without cumulus cells developed to blastocysts significantly less often than those cultured with added cumulus cells, 3 vs 38% of cleaved ova (P < .05). Co-culture of embryos with cumulus cells during the first 48 h only, or for the duration of the culture period, resulted in development rates similar to those of controls that were not vortexed. In Exp. 2, denuded zygotes were centrifuged (15,850 x g, 3 min) at room temperature to facilitate visualization of pronuclei. Centrifuged zygotes were either placed directly into conditioned medium for culture (with or without added cumulus cells) or DNA was first microinjected into their cytoplasm or a pronucleus. All microinjected embryos were co-cultured with added cumulus cells. Centrifugation and microinjection did not reduce viability significantly when embryos were co-cultured with cumulus cells. Development was reduced significantly when embryos were cultured without cumulus cells. Thus, when oviduct epithelial cell-conditioned medium was used, cumulus cell co-culture was beneficial during the early cleavage stages of in vitro-derived zygotes, including those that received DNA microinjection.