The heat shock response of growing and fully grown pig oocytes was analyzed in vitro by determining heat shock protein (HSP70) synthesis under both normal conditions (39 deg C, 0 and 6 h) and after heat shock (43 deg C, 1, 4 and 6 h). The results indicate that growing oocytes are able to synthesize HSP70 and this ability declines at the end of the growth period, and fully-grown oocytes are unable to induce HSP70 synthesis after heat shock. HSP70 is synthesized and stored during oocyte growth. The high HSP70 synthesis in non-heat-treated growing oocytes and a great amount of HSP70 in fully-grown oocytes support the hypothesis that HSP70 is important for oocyte growth and maturation.