Previously, overexpression of anti-apoptotic proteins, such as E1B-19K and Aven, was reported to alter lactate metabolism of CHO cells in culture. To investigate the effect of Bcl-x(L), a well-known anti-apoptotic protein, on lactate metabolism of recombinant CHO (rCHO) cells, two antibody-producing rCHO cell lines with regulated Bcl-x(L) overexpression (CS13*-0.02-off-Bcl-x(L) and CS13*-1.00-off-Bcl-x(L)) were established using the Tet-off system. When cells were cultivated without Bcl-x(L) overexpression, the specific lactate production rate (q(Lac)) of CS13*-0.02-off-Bcl-x(L) and CS13*-1.00-off-Bcl-x(L) were 7.32 +/- 0.37 and 6.78 +/- 0.56 pmol/cell/day, respectively. Bcl-x(L) overexpression, in the absence of doxycycline, did not affect the q(Lac) of either cell line, though it enhanced the viability during cultures. Furthermore, activities of the enzymes related to glucose and lactate metabolism, such as hexokinase, glucose-6-phosphate dehydrogenase, lactate dehydrogenases, and alanine aminotransferase, were not affected by Bcl-x(L) overexpression either. Taken together, Bcl-x(L) overexpression showed no significant effect on the lactate metabolism of rCHO cells. (c) 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1594-1598, 2013