Adventitious infections among rodents used in biomedical research and teaching continue to be problematic even with improved housing and disease-deterrent methodologies. In addition to well-documented viral diseases (e.g., mouse hepatitis virus and rodent parvoviruses) and parasites (mites and pinworms), new pathogens such as murine norovirus have emerged in recent years. Infectious agents can enter colonies via incoming rodent shipments, in unscreened biological materials, on people (especially husbandry or investigative staff) who move from a location where animals have a lower health status to an area where health status is higher and operational procedures are more stringent, or by introduction of contaminated food, bedding material, or other fomites. These factors, coupled with the very high volume of movement of rodents within and between institutions, increase the risk of spreading infectious agents. The challenge to the laboratory animal community is to implement control measures that halt the passage of these organisms from one location to another while still enabling collaborative scientific discovery to proceed with minimal disruption. It is therefore critical to make appropriate decisions about identifying outbreaks in a timely fashion and controlling the spread of infection once identified. Such efforts should be practical, reproducible, and cost-effective.