We isolated multiple HSPs from rainbow trout Oncorhynchus mykiss RTG-2 cells and quantitatively compared their mRNA levels between unstressed and heat-shocked cells using real-time RT-PCR analysis. Consequently, we isolated nine cDNAs encoding HSPs from heat-shocked RTG-2 cells, namely, Hsp90betaa, Hsp90betab, Grp78, Hsp70a, Hsc70a, Hsc70b, Cct8, Hsp47, and DnaJ homology. Quantitative RT-PCR analyses, in which Hsp70b isolated previously was included, showed that the mRNA accumulation levels of Hsp70a. Hsp70b, Hsc70a, Hsc70h, and Hsp47 were significantly increased after heat shock, and the increased levels of two Hsp70s, Hsp70a. and Hsp70b, were most conspicuous. In the case of Hsc70s, the increased level of Hsc70b was more remarkable than that of Hsc70a. These results demonstrate the importance of a comprehensive expression analysis of HSPs for better understanding of the cellular stress response in fish, especially in tetraploid species such as rainbow trout. (C) 2005 Elsevier Inc. All rights reserved.