Kitasato obtained a pure culture of the tetanus bacillus, Cl. tetani.

Antitoxins and their immunizing powers were discovered when Behring and Kitasato published their paper dealing with immunity to tetanus and diphtheria. This work laid the foundation of all future treatment with antitoxins, and was the basis of serotherapy. The paper was reprinted in the same journal, 1940, 66, 1348-49. Part 2, which deals with diphtheria, is by Behring alone. English translation in Bibel, Milestones in immunology (1988).

In 1901 Behring was the first recipient of the Nobel Prize for Physiology or Medicine "for his work on serum therapy, especially its application against diphtheria, by which he has opened a new road in the domain of medical science and thereby placed in the hands of the physician a victorious weapon against illness and deaths."