This book is a collection of data on the tenacity in the environment of bacteria and some rickettsiae important in medicine and veterinary medicine. These data are of fundamental importance to physicians, veterinarians, epidemiologists and others when, in their practices, they are confronted with epidemics of contagious diseases or outbreaks of foodborne illnesses. At such times prompt answers are often needed to limit the problem, and thus to protect the public's health. Since data needed for such a purpose are widely distributed in the internatio- nal scientific literature, the occasional desperate literature search is likely to miss some of the information that is available. This book seeks to fill that void. It lies in the nature of a compilation such as this is that it can never be totally complete. The compilation requires continual up-dating to include new information, and some currently acceptable information may have to be corrected as new data become available. However, most of the information in this compilation will never be out-of-date. The authors are always thankful for suggestions from others. Collection of the data in this book resulted from, first, several decades of studying the literature, and, second, literature searches made by the Institut fUr Dokumentationswesen in Frankfurt a. M., the Biomedi- zinische Datenbank of Hoechst A. G.