HLA-G is a non-classic class I MHC molecule specifically expressed by human invasive cytotrophoblast cells, which has been suggested to play a role in facilitating the immune tolerance of the conceptus. So far, very little is known about the regulation of the human HLA-G gene. The present study was, thus, designed to investigate the regulation of the human HLA-G promoter. JEG3 choriocarcinoma cells, which express HLA-G endogenously, were used as a model. A 890 bp fragment of the human HLA-G promoter was amplified by nested PCR from genomic DNA, cloned into pCR-Script and, after sequencing, subcloned into pGL3-Luc in front of the luciferase reporter gene. This vector was then used in transient transfection experiments in JEG3 cells. Parallel transfection experiments were performed using an alpha subunit (alphaSU)-Luc reporter plasmid as a control. Using this system, several potential modulating substances were tested in different concentrations and for different periods of time: phorbol ester (TPA), cAMP, IFNgamma, IL-1, and leukemia inhibitory factor (LIF), with only LIF administration resulting in induction of the HLA-G promoter. LIF treatment also resulted in induction of HLA-G mRNA. JEG3 cells are shown to possess LIF receptors. LIF is a pleiotropic cytokine produced at the maternal-fetal interface which has been shown to play an essential role in implantation in mice. LIF is produced in high amounts by the human endometrium and the trophoblast itself, and LIF receptors are present on cytotrophoblast cells. LIF could, thus, play a role in modulating HLA-G production and immune tolerance at the maternal-fetal interface.