Safe working practices and patient safety are of critical importance in the administration of blood transfusion. While the use of information technology has been proposed to ensure the safety of this process, the usability of such systems has not previously been studied. We present the results of a usability evaluation of an electronic clinical transfusion management system being piloted by the National Health Service in England. A number of major usability problems were recorded, largely relating to unnecessary action, limiting user control and recovery from user error. Such problems can, however, be resolved by relatively minor changes to system functionality and design.