Murine myelomas are rare cell variants deficient in inducible isoform of Hsp70 that protects cells from injury. In these cells Hsp70 is absent and is not induced under stress conditions. In this study myeloma cells NS0/1 were transfected with hsp70, and their susceptibility to apoptosis was challenged by serum deprivation or hydrogen peroxide. Expression of Hsp70 in NS0/1 cells made them more resistant to apoptosis in serum-free medium but did not affect their response to hydrogen peroxide. Hsp70 involvement in the protection of myeloma cells from apoptosis caused by different agents is discussed.