Overexpression of bcl-xL in recombinant Chinese hamster ovary (rCHO) cells has been known to suppress apoptotic cell death and thereby extend culture longevity during batch culture. However, its effect on specific productivity (q) of rCHO cells is controversial. This study attempts to investigate the effect of bcl-xL overexpression on q of rCHO cells producing erythropoietin (EPO). To regulate the bcl-xL expression level, the Tet-off system was introduced in rCHO cells producing EPO (EPO-off-bcl-xL). The bcl-xL expression level was tightly controlled by doxycycline concentration. To evaluate the effect of bcl-xL overexpression on specific EPO productivity (q(EPO)) at different levels, EPO-off-bcl-xL cells were cultivated at the two different culture temperatures, 33 degrees C and 37 degrees C. The q(EPO) at 33 degrees C and 37 degrees C in the presence of 100 ng/mL doxycycline (without bcl-xL overexpression) were 4.89 +/- 0.21 and 3.18 +/- 0.06 mu g/10(6) cells/day, respectively. In the absence of doxycycline, bcl-xL overexpression did not affect q(EPO) significantly, regardless of the culture temperature, though it extended the culture longevity. Taken together, bcl-xL overexpression showed no significant effect on the q(EPO) of rCHO cells grown at 33 degrees C and 37 degrees C. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 25: 252-256, 2009