Distribution of apoptotic cells and expression of the apoptosis-related factors p53, bcl-2 and bad during morphogenesis of the murine palatine rugae (PR) were examined histochemically using the terminal deoxynucleotidyl transferase-mediated UTP nick end-labeling (TUNEL) technique and specific antibodies against apoptosis and cell cycle-related molecules. Formation of the PR rudiment was controlled by cell proliferation and apoptosis in the palatal epithelium. TUNEL-positive cells were detected only at the epithelial placode area at 12.5-13.5 days post coitus (dpc), but only a few cells were positive at the protruding PR area at 14.5-16.5 dpc. Bcl-2 protein was expressed mainly in the areas outside of those containing TUNEL-positive cells at 15.5 -6.5 dpc. P53 protein was not detected throughout gestation. Bad was detected in the epithelial layer at 13.5 and 15.5 dpc and overlapping the apoptotic area at 13.5-15.5 dpc. Apoptosis of palatal epithelial cells might therefore involve spatiotemporally regulated expression of bad during murine PR development.