The effect of simple and sequential embryo culture media on the preimplantationdevelopment of mouse nuclear transfer (NT) embryos reconstructed with cumuluscell nuclei using a mechanical NT technique was studied. Blastocyst formation ratewas evaluated using CZB medium. Nonmanipulated and sham-manipulatedparthenogenetic embryos served as controls for, respectively, the medium and thehandling technique. Rates of blastocyst formation for medium and handling controlembryos were similar in CZB (50% and 53%). Development of NT embryos wassignificantly impaired from the two-cell stage onwards, reaching the blastocyst stage ata rate of 4% in CZB. These data demonstrate not only that NT embryos are moresensitive to in vitro culture conditions than parthenogenetic control embryos but alsothat selection of culture media can influence the preimplantation development of NTembryos.