A rare blood group and the associated anti-red cell antibody against a very common blood group factor make it significantly more difficult to find suitable red cell products, possibly endangering the additional treatment of the patient. The need of rare blood should be anticipated early enough. The availability of red cells is secured by extensive blood group studies among blood donors, by donor registers, freezing of rare red cells and through international collaboration. The determination of rare blood groups by genotyping provides a longed-for addition to the investigational repertoire of both patients and blood donors. Systematic freezing of red cells was started in Finland in 2010.