Immunofluorescence assay of cellular Bcl2. Two hundred thousand cells bound to polylysine-coated 35-mm Costar dishes were washed with PBS and fixed in 3.7% formaldehyde in PBS, rinsed again with PBS, blocked with 1% BSA/0.1% saponin, and reacted with monoclonal anti-Bcl2 antibody in 1% BSA/0.1% saponin/PBS. Cells were again rinsed with PBS and bound antibody detected with rhodamine conjugated goat anti-mouse Ig. After a final rinse with PBS and postfixing in 3.7% formaldehyde, dishes were mounted in glycerol:PBS and examined under a Zeiss Axioplan epifluorescence microscope. Magnification is × 350; scale bar represents 17 μm. (A) HL60; (B) HL60/VCR; (C) HL60BclX_L .