High levels of human bcl-2 protein(s) result in (i) the tumorigenic conversion of mouse NIH3T3 cells, (ii) the better survival of mouse myeloid cells in the absence of the required growth factor and (iii) give a growth advantage to human EBV-lymphoblastoid B cells both in low serum medium and limiting dilutions. The effect of the high levels of bcl-2 protein in EBV-B cells was further investigated. This revealed that high levels of bcl-2 alpha protein made EBV-B cells more resistant to a variety of stresses including the application of heat shock, ethanol, methotrexate and the absence of serum. Stress resistance was not observed in EBV-B cells with elevated level of c-myc protein. The mechanism of stress resistance conferred by the bcl-2 alpha protein is yet to be determined although the resistance does not seem to be the result of an increase in major heat shock proteins, hsp70 and hsp90, nor the arrest of cells in G1/G0 phase. The increased viability was observed in control transfectants but not in bcl-2 transfectants when cells are seeded at higher density in the absence of serum. Thus the improved survival of cells as a result of high levels of the bcl-2 alpha protein is not specific to the absence of growth factor but is found to occur with a variety of stresses.