A 44 year old Caucasian female was investigated as a possible living unrelated donor for a 25 year old Caucasian female. As part of the pre-transplant work-up, HLA AB/DR typing was performed (Genovision PCR-SSP). Typing results identified multiple alleles at all loci. Alleles identified included A*01,02,11,36; B*08,44,27,51; DRB*0103,03(17),04,13; DRB3* and DRB4*positive, and DQB1*02, 0301, 0302, 06. Serological typing results, which did not express the chimeric antigens, were A2,11;B44,51. To rule out contamination and/or sample mix-up, typing was repeated with a newly extracted DNA sample and with a new sample collected the following week. All results were identical. This individual was ruled as a potential donor due to a positive B cell crossmatch. The recipient has Class II antibodies to DR4,7, and 53. Both DR4 and DR53 were two of the DR antigens in the potential donor. It has been documented in the literature that cells travel in both directions between the fetus and mother during pregnancy with fetal microchimerism found to be more common than maternal chimerism. Recent studies have shown that fetal cells, including progenitor cells, have been found to persist in the peripheral blood of mothers for decades after childbirth, and maternal cells have been found in the blood of their children as old as 49 years. A review of the donor's history was negative for blood transfusions, previous transplants, autoimmune diseases, and liver disease. She did report six pregnancies with five live births and one miscarriage. This was the first case of microchimerism seen in our lab during 10 years of molecular based typing. HLA typing of this donor's husband and children is needed to confirm fetal or maternal microchimerism.