Presence of aspirin in blood units

2,655 blood units collected from healthy voluntary donors selected according to the criteria of the International Society of Blood Transfusion were tested for the presence of aspirin. This drug was found in 6% of the samples at concentrations ranging from 10 to 200 microgram/ml. The clinical implications of these findings are discussed. We also report a case of allergic reaction which could probably be related to the transfusion of blood containing aspirin.