Effects of elevated in vitro temperature on in vitro produced early bovineembryos were analysed in order to determine its impact on the expression ofheat shock protein 70 (hsp70). In vitro matured bovine oocytes, 2-cell and8-cell embryos, and day 9 hatched blastocysts subjected to control andelevated temperature conditions were analysed by semiquantitative reversetranscription polymerase chain reaction methods for hsp70 mRNAexpression. Results revealed the expression of hsp70 mRNA under controlconditions and that early embryos can respond to heat stress by transcribinghsp70 mRNA. Confocal laser scanning microscopy used to localise the hsp70protein in oocytes and embryos revealed that the distribution of hsp70 inthe ooplasm of immature and mature oocytes is unaffected by exposure toelevated temperatures and that this protein was closely associated with themeiotic spindle, indicating its possible role in stabilising thisstructure. In 8-cell embryos derived under control conditions, hsp70 wasevenly distributed in the cytoplasm but appeared as aggregates in someembryos exposed to elevated temperature. In heat-stressed hatchedblastocysts, a more even distribution was noted following heat stressrelative to corresponding controls, indicating their competence to respondto elevated temperature.