To ensure our animals are healthy and disease-free all colonies are maintained in an environment with a high level of biosecurity. A large proportion of our mice are housed in individually ventilated cages which prevents the transfer of potential infections from one cage to another. Routine health surveillance is carried out on all of our animals. In order to maintain the health status of animals in the Biological Services Unit (BSU), a number of controls on movement of animals, people and biological products are necessary. Microbiological health monitoring in laboratory rodents is an important consideration in animal studies. Maintaining a high health status in our animals therefore facilitates good welfare and good science.