In our historical imagination, penicillin plays the role of the good sister of the atomic bomb. It epitomizes the success of the U.S. scientific mobilization and the emergence of modem biomedicine. This chapter discusses the fate of penicillin in France and Germany, comparing the reactions of the two countries to the antibiotic challenge under restricted conditions. The comparison centers on the scientific and industrial practices that created penicillin. It also sheds light on the professional styles, forms of expertise, and political resources that helped shape the meanings and uses of the antibiotic. The French section recounts how the Pasteur Institute and the military administration organized penicillin research and production during 1945-1947. The alliance between the two has roots in the highly peculiar political and social climate of the liberation and in the biotechnological tradition of the Pasteur Institute. The German section focuses on the Kaiser Wilhelm Institute for Biochemistry. The study of the institute, which worked closely with a pharmaceutical company, features the interplay between academic chemists and industry, while providing insights into the research organization under National Socialism.