The development of increased bacteriologic and viral screening has revealed evidence of exposure to possible pathogens in animals from even the best suppliers. Because the cost in money and space to quarantine all rodents in many types of research institutions is great, and because of an increased ability to detect possible pathogens, a dilemma exists. At the same time, regulations are being implemented which, in many cases, mandate a quarantine period. In all cases, however, the professional judgement of laboratory animal medicine specialists is increasingly needed to interpret the best course of action. A proper matching of animal quality with a realistic assessment of research requirements seems the best course, with quarantine implemented where truly appropriate.