['Microchimerism may play a part in transfusion complications. The aim of this study was to examine whether establishment of post-transfusion microchimerism was related to leukocyte content.', 'Twenty non-pregnant female patients, without known malignant or immunological diseases, mean age 68 years, receiving 2-4 units of red blood cell concentrates during elective surgery, were included. One or two of the units were from male donors. Ten patients received buffy-coat depleted red blood cell concentrates, leukocyte count 108-109 per unit, and 10 patients received red blood cells leukoreduced by prestorage leukocyte filtration, with a leukocyte count of <106 per unit. EDTA samples were collected in vacuum tubes before and after 1 week and 6 months after transfusion. The tubes were frozen and stored at -400 degrees C. Genomic DNA was isolated and PCR performed using four primer sets amplifying markers on the Y-chromosome.', 'Microchimerism was detected in a total of eight out of the 20 patients. In three patients microchimerism was detected only before transfusion. These patients had given birth to one or two boys each, and had no history of previous transfusion. Two patients receiving buffy-coat depleted red blood cell concentrates and two patients receiving leukoreduced red blood cell concentrates had detectable microchimerism 1 week after transfusion. The age of the transfused red blood cell concentrates was 6, 24, 8 and 7 days, respectively. One patient receiving leukoreduced red blood cell concentrates had detectable microchimerism after 6 months. The age of this concentrate was 22 days.'] Does microchimerism in immune competent patients related to the leukocyte content of transfused red blood cell concentrate?