Ruth Ann Sanger's scientific career was concerned with the delineation and mapping of human blood group genes by simple manual methods using, as tools, blood group antibodies and the agglutination reaction followed by statistical analysis of the results. Her active period coincided with the flowering of the whole subject of blood groups, which was initiated by the recognition of the clinical significance of the Rh antigens and the rediscovery of the antiglobulin reaction by Coombs, Mourant and Race (Coombs et al. 1945). In these days of ‘high-technology’ research, it is salutary to recognize that the complex body of knowledge that has been accumulated about blood groups has been derived by using the very simple technique of the visible cross-linking of red cells by antibodies specific for the blood group antigens present on the red cell surface. Landsteiner had by chance discovered the ABO blood group system in 1900 with the use of the agglutination reaction, but little progress was made in the next 45 years and we now know that the main reason for this is that most blood group antibodies are not physically capable of bringing about the cross-linking and agglutination of red cells on their own. This problem was solved by the introduction of the antiglobulin reaction, which uses a secondary antibody to bring about the cross-linking of blood group antibodies already attached to red cells.