On March 14th of this year, the birthday of Paul Ehrlich, the great German researcher and ‘founder of chemotherapy’, returned for the 150th time. Interestingly, his later colleague Emil von Behring was born one day later in 1854. Both were coworkers in Robert Koch’s laboratory and became Nobel Prize laureates (for their work in immunology), making great contributions to antiinfectious treatments. Emil von Behring’s approach was through the use of immunological agents, while Ehrlich favored an approach of antiinfectious treatment by chemical agents. Through an ingenious concept that was a clear continuation of his early days in research with dyes, he found the first chemotherapeutic agents. From his dye work, he had concluded the following: if there are dyes that one can use to stain cells, why not develop pharmacological agents that, like stains, also attach to a structure in the living pathogen and kill them. He gave these agents the emotionally charged name ‘magic bullets’. This introductory review will initiate a series of papers on the occasion of Ehrlich’s 150th birthday and the ‘World Conference on Dosing of Antiinfectives: Dosing the Magic Bullets’, which is going to be held in Nürnberg, Germany, from September 9 to 11, 2004 (see www.ehrlich2004.org). Apart from the conference topic, this conference will also commemorate a real science giant of the last century and yet a modest human being whom, as Robert Koch put it, ‘one had to like’. This article recalls Ehrlich’s ingenious concepts, including modern syphilis treatment, one-dose treatment (‘therapia magna sterilisans’) of Helicobacter pylori infections and introduction of an arsenic compound, arsenic trioxide, as well as experiments and new exciting data on Congo red, a well-known ‘non-Ehrlich dye’.