Graft Versus Host Disease (GVHD) remains a major cause of morbidity and mortality in allogeneic stem cell transplantation (SCT). The MLC assay has been generally accepted as a standard test for determining HLA-D region compatibility. In this study, the MLC test has been carried out on the related recipient-donor couple who were prepared for allogeneic SCT and were found to be matched for HLA-A, -B, -Cw, DR, DO but not for -DP. The result of the MLC test was positive. We observed that HLA-DP mismatch was responsible for the increased proliferation values in MLC test.