BMP4 and embryonal carcinoma: Different behaviours of various cell lines under the same experimental conditions have been shown previously.14 Similarly, serial sections of the EBs derived from S2 embryonal carcinoma cell line cultured in the presence of BMP4 revealed more small cavities located near the periphery of the EBs due to the cell death.7 Our data also indicated that seeding a higher cell density in hanging drops also led to the formation of a central cavity in B1.