The pig exhibits true epitheliochorial placentation, where the fetal membrane maintains attachment throughout pregnancy but does not invade into the maternal uterine endometrium. Accordingly, the expression and function of cell adhesion molecules are very important for embryo implantation and the establishment of pregnancy. In our recent microarray analysis, we found that activated leukocyte cell adhesion molecule (ALCAM) was expressed in the uterine endometrium during pregnancy in pigs. To better understand the roles of ALCAM in the establishment and maintenance of pregnancy, we examined ALCAM expression in the uterine endometrium during the estrous cycle and pregnancy in pigs. Real-time RT-PCR analysis showed that ALCAM was differentially expressed in the uterine endometrium during the estrous cycle and pregnancy, with the highest levels on D12 of pregnancy. ALCAM mRNA was localized to the luminal and glandular epithelial cells and to the trophectoderm of conceptuses during early pregnancy. The steroid hormones estrogen and progesterone had no effect on ALCAM expression in an endometrial explant culture study. Further, we found that ALCAM expression in the uterine endometrium from gilts with somatic cell nuclear transfer-derived embryos was not different from that in gilts with embryos from natural mating. ALCAM was expressed in a pregnancy stage- and cell type-specific manner in the uterine endometrium and conceptuses during pregnancy. These findings suggest that ALCAM may play a role in the establishment of pregnancy. Further analysis of ALCAM will provide insight into the implantation process and establishment of pregnancy in pigs.