Abstract
The Swedish scientist Örjan Ouchterlony published four ground-breaking papers 1948-1966 in Acta Pathol Microbiol Scand where he described a new method of antigen-antibody reactions in gel. He described and defined the 'reaction of identity' and 'reaction of partial identity' when he used related antigens and 'reaction of non-identity' when he used non-related antigens. His results inspired scientists in other countries to further develop and modify the 'Ouchterlony method' which became useful for both scientific and clinical purposes. This survey describes how the methods were discovered and how they became modified and improved and how they were used, but also underlines that the original Ouchterlony method is still used.