Objective: Many functional characteristics of human leukocyte antigen G (HLA-G) support the notion that it plays an important role in maternal immune tolerance to the fetus. Previously. we reported that HLA-G protein and mRNA levels are enhanced by progesterone in vitro through activation of HLA-G gene transcription. Since we could not find any previously reported progesterone response element (PRE) sequences within the HLA-G gene promoter region, the objective of this study was to identify any novel progesterone response elements in this region.