Emil Behring had worked at the Berlin Institute of Infectious Diseases until 1893 on developing an antiserum for treating diphtheria and tetanus but with inconsistent results. Koch suggested that Behring and Ehrlich cooperate on the project. This joint work was successful to the extent that Ehrlich was quickly able to increase the level of immunity of the laboratory animals based on his experience with mice. Clinical tests with diphtheria serum early in 1894 were successful and in August the chemical company Hoechst started to market Behring’s “Diphtheria Remedy synthesized by Behring-Ehrlich.” The two discoverers had originally agreed to share any profits after the Hoechst share had been subtracted. Their contract was changed several times and finally Ehrlich was eventually pressured into accepting a profit share of only eight percent. Ehrlich resented what he considered as unfair treatment, and his relationship with Behring was thereafter problematic, a situation which later escalated over the issue of the valency of tetanus serum. Ehrlich recognized that the principle of serum therapy had been developed by Behring and Kitasato. But he was of the opinion that he had been the first to develop a serum which could also be used on humans, and that his role in developing the diphtheria serum had been insufficiently acknowledged. Behring, for his part, schemed against Ehrlich at the Prussian Ministry of Culture, and from 1900 on Ehrlich refused to collaborate with him. von Behring was the sole recipient of the first Nobel Prize in Medicine, in 1901, for contributions to research on diphtheria.