Cigarette smoke extract caused necrosis with no or little evidence of apoptosis in human lung cancer cells (H1299). Human lung cancer cells (H1299) were treated with media alone (control) and various concentrations of CSE; a) control, b) CSE (1.0%), c) CSE (2.5%), d) CSE (5.0%), e) CSE (7.5%), f) CSE (10%) for 24 hr. The cells were stained with ethidium bromide and acridine orange and observed under fluorescence microscopy. Living cells had normal shaped nuclei with green chromatin. Early apoptotic cells have shrunken green nuclei with chromatin condensation, whereas necrotic or late apoptotic cells had normal/condensed nuclei that were brightly stained with ethidium bromide and appeared red. Percentage of viable (white bars), apoptotic (grey bars) and necrotic/late apoptotic (black bars) determined by counting as described in Materials and Methods. Results are mean of 3 experiments ± SEM. *p < 0.05, and §p < 0.001 compared with control group. L = Live; A = Apoptosis; N = Necrosis.