Successful in vitro development of embryos is dependent upon maintenance of cellular function in the embryonic microenvironment. However, the molecular aspects involved in the thermoprotection of embryos, against heat and cold stress it is not clear. The aim of this study was to determine the effects of heat and cold shock on the viability and development of porcine diploid parthenotes developing in vitro. Exposure of two-cell stage embryos to 41 degrees C did not affect further cleavage. However, prolonged heat shock, greater than 12h, reduced the percentage of blastocysts that developed from two-cell stage parthenotes, as well as the total number of nuclei in the blastocysts that formed. Furthermore, the degree of apoptosis was increased (P<0.05) in these blastocyst stage parthenotes. In contrast, exposure of two-cell parthenotes to cold (30 degrees C) for 24h did not affect the cleavage rates, development to blastocyst, nor the total cell numbers per blastocyst. Real time PCR revealed that quantitative expression of the Bcl-xL gene was not different, but amounts of HSP 70.2, Bak, and Caspase 3mRNA were significantly increased in the heat shocked embryos, as compared with untreated controls. These results suggest that porcine embryos are more tolerant to cold shock than to heat shock. Heat stress seems to induce apoptosis related gene expression in porcine parthenotes developing in vitro, which results in diminished parthenote viability.