In this article we show that long-term cultivation of Chinese hamster fibroblasts of line V-79 RJK at elevated temperature resulted in the selection of variants with genetic changes at the level of karyotype. From the first steps of resistance selection to elevated temperature we identified population of cells with changes in karyotype (polyploidy cells, deletions, inversions, translocations of chromosomes, and some cells with DM-chromosomes). Further cultivation was accompanied with selection of cells with paracentrical chromosome breakages and HSR's on chromosomes. Nonspecific destabilization of the karyotype (on first steps of selection) was associated with increased expression of hsc70 and pgp. After long-term incubation at an elevated temperature, the cells with karyotypic changes had the basal level of hsc70 and pgp expression.