Mouse secondary palate morphogenesis is accompanied by distinctive patterns of proliferation in the palatal epithelium which latterly reflect its region-specific differentiation into oral, nasal and medial edge phenotypes. Isolated intact embryonic palatal epithelial sheets were cultured prior to, and during, the critical period of epithelial differentiation in chemically defined culture medium with, and without, 10% donor calf serum. The spatial and temporal patterns of proliferative activity were investigated by immunocytochemistry in 'pulse' and 'continuous' labelling experiments using bromodeoxyuridine (BrdUrd). Continuously labelled cultures exhibited extensive proliferation throughout the oral, nasal and medial edge regions. Pulse labelled cultures demonstrated a shift in mitotic activity from nasal to oral epithelial cells probably representing the cell turnover associated with the respective differentiated phenotypes. Medial edge cells became post-mitotic within the first 19 h of culture. Our defined culture system coupled with the immunocytochemical detection of cell proliferation using BrdUrd offers a rapid and precise method for the further investigation of palatal epithelial proliferation and its regulation by extrinsic factors.