Die Wertbestimmung des Diphtherieheilserums.

Ehrlich improved Behring’s diphtheria antitoxin through quantitative titration and established an international standard for this and other antitoxins. This was the beginning of the concept of biological standardization. The first exposition of Ehrlich’s side-chain theory appeared in this paper. Abridged English translation in Bibel, Milestones in immunology (1988).

In 1908 Ehrlich shared the Nobel Prize in Physiology or Medicine with Metchnikoff "in recognition for their work on immunity." See also Nos. 14167 and 12438.