The increased use of microorganisms as experimental objects for detailed studies of various biological phenomena has led to impressive advances in their interpretation in molecular terms. This has resulted in a tendency to equate microbiology with "molecular biology." In the author's opinion this attitude is unfortunate, because it fails to direct attention to the importance of microorganisms for the study of problems that are as yet, inaccessible to the approaches of molecular biology. The enormously diverse microbial world offers numerous opportunities for exploratory studies of complex problems on a non-molecular level, particularly as they related to levels of organization of component parts and interactions among them and with the environment. Such investigations can eventually provide the molecular biologist with material for more refined analysis. A plea is made for the perpetuation and extension of broad biological approaches to microbiology, in which the potential advantages of diverse kinds for ...