The proposed research will test the feasibility of using inexpensive polymeric membranes to serve as passive contaminant barriers for laboratory animals. Theoretical calculations show that the flux of animal respiratory gases through polymeric membranes can be more than sufficient to support life for animals in hermetically sealed environments. These membranes could be used to protect animals from airborne pathogens while permitting the rapid passage of atmospheric gases necessary for respiration. Besides protecting animals from extraneous contamination, they can be used to protect laboratory personnel from allergens and infectious agents. Membranes, supported on porous substrates should be useful for animal containment systems in research, breeding, housing, and shipping of research animals throughout the United States. The resulting technology will provide an economical means to control environmental variables encountered in animal housing. Research will focus on developing an optimal membrane/support combination. Membrane/support combinations will then be tested for gas exchange with live animals and for barrier effectiveness in microbial challenges.