The results of three months of testing using rodents in a breadboard biological isolator cage are presented. These cages are designed to provide isolation using microbial air filters on both inlet and outlet. Four different types cf filters were tested: a conventional HEPA filter (rated at 99.97% efficient at 0.3 microns), a “hospital” grade HEPA filter (95% efficient at 0.3 microns), and two grades of “Filtrete” - a proprietary 3M polypropylene material (rated at 84% and 97.3%, respectively, at 0.3 microns). Test results showed excellent performance on all filters, meeting or exceeding the strict particulate and microbial air quality standards proposed for the outlet of the animal holding facility: Class 100 and 10 Colony Forming Units (CFU)/m3. In addition, it was also discovered that the fiberglass batting used inside the cage to contain animal waste served as an effective microbial filter by itself.