Multinucleated variant endothelial cells (MVECs) generally exist in atherosclerotic human aorta and even in nonatherosclerotic aorta. Because the number of nuclei is increased in every MVEC, and because DNA instability was suspected, a series of oncogene expressions was conducted to clarify the nature of nuclear abnormality. The tumor suppressor gene p53 was found to be specifically expressed in the multinuclei of MVECs, while double nuclei were sometimes positive, and mononuclear typical endothelial cells were always negative for p53. Polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) revealed extra bands in exons 5 and 7 of the p53 gene, but no additional band in exons 6 and 8. In a BCL family, BCL-2 was coexpressed in one or two nuclei in the perinuclear space of the multinuclei of MVECs, whereas MCL-1, BCL-XS/L, and BAX were all negative, indicating that the BCL-2 coding gene is expressed only in the corresponding one or two nuclei of the multinuclei. Another oncogene, c-MET (hepatocyte growth factor receptor), was universally expressed in either type of endothelial cells, but other oncogenes, k-RAS and c-ERBB2, were not expressed in either type. MVECs were derived from human aorta and therefore non-tumorous somatic cells. No morphologic evidence of apoptosis was found. Although it is unclear that the extra bands came from the MVECs or just from ECs associated with atherosclerosis, combined immunocytological studies and PCR analysis suggest that MVECs express mutant type p53.