The relative frequency of Kell (K:1) antibodies in pregnant women and a series of cases of Kell hemolytic disease of newborns were evaluated to review the strategy of managing potential disease. Among reproductive-aged women, Kell antibodies are about 60% as frequent as Rho(D) antibodies, but Kell disease is only 3% as common as Rhohemolytic disease. The reason is related to frequent transfusion- alloimmunization by Kell antigen and the low frequency of the K:1 gene among fathers. Kell hemolysis is severe in about half of cases. Amniocentesis is indicated in only a few circumstances: previous child with erythroblastosis fetalis, significant increase in maternal Coombs titer, presence of Kell antigen in the father, and after comparison, of the relative risks of hemolytic disease and amniocentesis in each patient. Screening for Kell antigen before transfusing premenopausal women would be a means of avoiding erythroblastosis, but the rarity of severe disease does not justify this approach.