Stress proteins are induced in response to a wide range of biological and physicochemical stresses; HSC70 (constitutive) and HSP70 (inducible) belong to the HSP70 stress protein family. The present study aimed at investigating whether environmental stress, particularly thermal and oxidative stress, is involved in modulating HSP70/HSC70 expression in in vitro porcine embryos from two/four cell stage to blastocyst. For oxidative stress, embryos were cultured at 38.5 degrees C under a 5% O2-5% CO2 atmosphere or 5% CO2 in air (approximately 20% O2); for thermal stress, embryos were cultured at 38.5 degrees C under 5% O2, 5% CO2, and exposed to heat shock (1 hr at 42 degrees C). At the end of culture, embryos were analysed by Western blotting, using specific antibodies discriminating HSP70 from HSC70. Embryos cultured under 20% O2 showed HSC70 levels significantly higher (P < 0.005) than embryos cultured under 5% O2, while heat shocked embryos presented HSP70 levels higher (P < 0.01) than control group. In addition, the developmental rate of embryos was negatively affected by the higher oxygen tension (P < 0.05). Our data indicate that porcine embryos express both HSP70 and HSC70 and could differentially respond to both oxidative and heat stress by up-regulating HSC70 and HSP70, respectively.