This volume represents the proceedings of a symposium at The Rockefeller University on October 23, 1989, in commemoration of the fiftieth anniversary of the discovery by Rene Dubos of gramicidin, the first antibacterial agent to be obtained from natural sources through rational pursuit. It also recalls other events leading to the beginning of the antibiotic era and effective antimicrobial therapy. The reports given reveal more than the bare facts of discovery; they paint a picture of the science and scientists of fifty years ago: interpersonal relationships, the competitive aspects of research, personal gain, and the role of industry.