On the basis of the actual knowledge on Lan antigen, the first example of anti-Lan in Polish population was described. This alloantibody found in the serum of Lan negative mother was responsible for the haemolytic disease of her newborn. Family study revealed two Lan negative members: the father and the brother of the proposita. This paper emphasizes the importance of screening for immune alloantibodies, performed in the sera of all women independently of their ABO and Rh blood groups, at early period of pregnancy.