Human leukocyte antigen-G (HLA-G) displays immunotolerogenic properties toward effector cells in graft rejection through inhibition of natural killer (NK) and cytotoxic T lymphocyte (CTL)-mediated cytolysis and CD4+ T-cell alloproliferation. CD4(+)CD25(+)(high) regulatory T (Treg) cells are pivotal for the maintenance of self-tolerance of pathogenic alloresponses after solid organ or bone marrow transplantation in murine model systems. The aim of this study was to investigate whether there was an association between soluble and membrane-bound HLA-G levels on Treg cells and liver graft prognosis. For this purpose, we studied 37 liver transplant patients and 13 healthy blood donors. To investigate the expression of HLA-G on the surface of peripheral mononuclear (PMNL) cells, we have used monoclonal antibodies in flow cytometry to estimate CD4, CD25, CD45, and HLA-G content. HLA-G serum levels were determined by ELISA. We observed a correlation between sHLA-G serum levels and liver function tests. After a month of HLA-G decrease in serum levels, liver function tests such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), direct bilirubin (DB), total bilirubin (TB), and alkaline phosphatase (ALP) were above normal levels, suggesting liver dysfunction or rejection. Considering these results, we concluded that the increased sHLA-G in serum and on cell surfaces may afford preliminary data on the prognosis and response to treatment in liver transplant patients.