The Wright (Wr(a)) antigen is found on the red blood cells of approximately 1 : 1000 Caucasians. Anti-Wr(a) has been reported to be present in 1 : 25 to 1 : 100 healthy blood donors and an even higher proportion of hospital patients. Incompatibility due to anti-Wr(a) might therefore be expected to occur in approximately 1 in 50,000 blood transfusions. Reports of haemolytic transfusion reactions (HTR) and haemolytic disease of the newborn due to anti-Wr(a) are, however, rare. We report an acute HTR due to anti-Wr(a) in a 58-year-old man with myelodysplastic syndrome associated with rigors, shortness of breath and a significant rise in serum bilirubin from 16 micromol L(-1) pretransfusion to 110 micromol L(-1) immediately afterwards. This was accompanied by the appearance of bilirubin and urobilinogen in his urine and a fall in haemoglobin of nearly 2 g dL(-1) following the transfusion. Anti-Wr(a) was the only antibody implicated. When tested against the recipients plasma, Wr(a+) panel cells and the transfused unit responsible for the reaction were 2-3+ by indirect antiglobulin test (IAT) and the donation typed as Wr(a+). The recipient had the common Wr(a-) phenotype. The reaction resulted in the patient being admitted to hospital for 2 days. The increasing use of electronic issue may result in more frequent reports of reactions due to anti-Wr(a) using current screening cells.