A case of alloimmunization in pregnancy caused by antibody to Kell red blood cell antigen is described. The baby was born prematurely with severe anaemia (HB 3g/dL). He was the 5th child of the family. The mother, who was found blood group O, Rh D positive, received at the age of 18 years a blood transfusion. This case emphasizes the importance of serological screening for low frequency red cell antigens, particularly in the case of a positive indirect Coomb's test in Rh positive pregnant mothers.