During 1988, our laboratory (The National Blood Group Reference Laboratory) detected clinically significant alloantibodies (excluding anti-D and anti-C + D) in samples from 72 patients from 24 different hospitals, transfusing about 40,000 units of red cells in this period of time. The simultaneous presence of autoantibodies complicated the serological diagnosis in a number of cases. Two patients had suffered acute haemolytic transfusion reactions due to antibodies not being discovered in the pretransfusion testing (anti-c and anti-Fya). 13 showed serological evidence of delayed haemolytic transfusion reaction not noted in the local hospital. We believe that delayed haemolytic transfusion reaction is seldom recognized. We stress the importance of quality control programmes in blood group serology.