1. This study demonstrated aloe-emodin- and emodin-induced apoptosis in lung carcinoma cell lines CH27 (human lung squamous carcinoma cell) and H460 (human lung non-small cell carcinoma cell). Aloe-emodin- and emodin-induced apoptosis was characterized by nuclear morphological changes and DNA fragmentation. 2. During apoptosis, an increase in cytochrome c of cytosolic fraction and activation of caspase-3, identified by the cleavage of its proform, were observed. 3. To elucidate whether the expression of protein kinase C (PKC) isozymes are involved in aloe-emodin- and emodin-induced apoptosis, this study examined the changes of PKC isozymes by Western blotting techniques during aloe-emodin- and emodin-induced apoptosis. 4. The expression of PKC isozymes involved in aloe-emodin- and emodin-induced apoptosis of CH27 and H460 cells. In this study, aloe-emodin and emodin induced the changes of each of PKC isozymes in CH27 and H460 cells. 5. The decrease in the expression of PKC delta and epsilon may play a critical role in aloe-emodin- and emodin-induced apoptosis in CH27 and H460 cells. 6. The present study also demonstrated that PKC stimulation occurs at a site downstream of caspase-3 in the emodin-mediated apoptotic pathway.