For more than a century, microbiologists have isolated non-virus microorganisms (nvms), notably bacteria, fungi (including yeasts) and protozoa from tumours and have suggested that they play a role as causal agents of most human cancers.  Every generation of microbiologists has isolated so-called “cancer germs”; some have claimed to have fulfilled Koch’s postulates in regard to cancer, while some have claimed that vaccines prepared from their isolates could reduce the symptoms, or even cure cancers. While Helicobacter pylori  has been shown to cause gastric cancer, the possibility that other bacteria and nvcs cause cancers continues to be surprisingly neglected; instead, most of the research effort into the role of infectious agents in cancer continues to be devoted to viruses. Here, both the historical and more recent literature linking nvms with cancer will be discussed; hopefully, the information provided will help focus attention on the role of these organisms as causal agents of cancer.