NCR-G3 cells were established from a testicular embryonal carcinoma and were differentiated into multi-lineages including trophectoderm cells by exposure to retinoic acid. The differentiated cells began to produce human chorionic gonadotropin (hCG), a trophectoderm-specific hormone, which was regulated at the mRNA level. As we assumed that genes responsible for differentiation were differentially expressed at the early stage of retinoic acid-induced differentiation, we prepared a cDNA library from retinoic acid-treated NCR-G3 cells. This cDNA library was then screened for genes whose expression was induced during the differentiation of these cells. From about 5 × 104 clones screened, three independent sequences were isolated. Sequencing analysis revealed that clone 1002 codes for mcll/EAT, which has a Bcl-2 homology domain. The expression of mcll/EAT, the Bcl-2 related gene, was increased at an early stage of the retinoic acid-induced differentiation and preceded the up-regulation of cytokeratin and hCG genes after ratinoic acid treatment. Furthermore, mcll/EAT was also up-regulated by heat shock, which has recently been shown to induce the cells to differentiate.