We reviewed 1500 acute transfusion reactions that were reported to the Auckland Regional Blood centre over a 7 year period, from approximately 440,000 transfusions. The majority of reactions were to red cells, and these had the highest reaction incidence per unit (0.73%) of all blood products. The reaction incidence per unit transfused for plasma was 0.1%, for stable plasma protein solution 0.01%, and for platelets 0.04%. The majority of symptoms reported were mild and transient. The commonest were fever (72%), rigors (33%), and rash or urticaria (30%). Although more serious reactions were reported such as angioedema, hypotension and pulmonary oedema, none of these were severe, as judged from the data reported to the centre. There were two transfusion related deaths during the study period, one due to an ABO incompatible transfusion, the other due to bacterial contamination of a unit of blood. Leucocyte agglutinins or antibodies were detected in 29% of those with a febrile reaction, but were also detected in 22% of those who remained afebrile. Serological abnormalities that may have accounted for the reaction were only detected in 12 patients six of whom had autoantibodies. As laboratory investigation reveals little that accurately defines the aetiology of a reaction, a rationalisation of the investigation into acute transfusion reactions is suggested.