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TB/C3 hybridoma cells were transected with either pEF‐MClneopA or pEF bcl2‐MClneopA vectors to produce a control cell line (TB/C3 pEF) and a cell line that overexpresses the “antiapoptotic” human bcl‐2 protein (TB/C3 bcl2). Flow cytometry analysis of intracellular bcl‐2 protein levels enabled near on‐line monitoring of the stability of bcl‐2 expression in the absence of drug selection. It was possible to maintain spontaneous selection of cells with the overexpression of bcl‐2 protein during semicontinuous cultures at very low dilution rates, where cells were subjected to the selective conditions of nutrient limitation and high toxic metabolite concentrations. Interestingly, cells that overexpressed bcl‐2 were adapted to suspension culture conditions significantly faster than control cells. Dual fluorescence staining with acridine orange and propidium iodide allowed for discrimination between viable, apoptotic …