The objective of the present study was to study the expression and localization of heat shock protein 70 (HSP 70) in the immune organs and ceils of heat stressed chicks. The results showed that high levels of HSP70 were expressed in thymuses, spleens, bursas of fabricius of conventional chicks. Furthermore, expression of HSP70 mainly took place in cytoplasms of thymus and spleen cells but in nuclei of bursas of fabriciu. Among tested organs, spleen cells steadily expressed HSP70. Under heat stress, the IOD of HSP70 in thymuses gradually decre...