Dr. Paul Ehrlich's family was so happy with Edward G. Robinson's portrayal of him that they gave Robinson a letter written by Dr. Ehrlich.
Paul Ehrlich's cure for syphilis, Salvarsan 606, became the most prescribed drug in the world until the discovery of penicillin in the 1940s, when it became the preferred treatment for the disease.
This film generated controversy because many thought the subject of syphilis too scandalous a topic for a motion picture in 1940.
Although not covered in the film, Dr. Paul Ehrlich also discovered the structural formula of atoxyl, a chemical compound used in the treatment of sleeping sickness.
Dr. Sahachiro Hata, portrayed in the film by Wilfred Hari, is co-credited with Dr. Paul Ehrlich in the development of Salvarsan 606.