Streptobacillus moniliformis (Sm), the causative agent of rat-bite fever and Haverhill fever in man, is also a pathogen in certain laboratory and domestic animals. With the introduction of modern maintenance systems, this microorganism seemed to be eradicated from laboratory animal units, but recent reports of Streptobacillus moniliformis (Sm) in colonies of laboratory rodents give evidence that this 'forgotten' bacterium can still be found even behind hygienic barrier systems. Although various national and international recommendations on microbiological screening include Sm, attempts to screen might fail because of insufficient knowledge about this remarkable bacterium. This article highlights these problems. As there is no recent review of Streptobacillus moniliformis, present knowledge of this zoonotic agent is summarized to include: description of the bacterium, its taxonomic position, host spectrum and clinical importance for animals and man, cultivation, diagnosis, antibiotic therapy, risk to laboratory personnel (occupational hazard) and geographical distribution.