Genetically defined and genetically engineered mice that express immunological deficiencies or develop autoimmune disorders are the models of choice for many researchers studying diseases such as diabetes, systemic lupus erythematosis, cancer and AIDS. Many investigators at The Jackson Laboratory (TJL), as well as investigators at numerous other institutions worldwide, depend on TJL's unique strains of immunodeficient and autoimmune mice for their research. Realization of the full research potential of these mice requires that they remain free of contaminating microorganisms, as exposure of these fragile animals to even generally innocuous microorganisms may cause: (1) disease, decreased longevity, and even death, (2) impaired breeding performance; (3) lesions or physiological alterations that can confound the interpretation of experimentally-induced changes; and/or (4) reduced expression of the critical phenotype. The objective of the project described in this application is to provide barrier housing for the pathogen-free maintenance of immunodeficient and autoimmune research mice within TJL's Research Animal Facility. Funds are requested to construct a new facility for immunodeficiency and autoimmunity research through the: (1) renovation and upgrading of existing conventional animal housing and laboratory space to provide barrier facilities for the housing and manipulation of immunodeficient and autoimmune mice; (2) purchase of pressurized individually-ventilated cage racks and laminar- flow. HEPA-filtered changing stations for housing and manipulation of these mice; and (3) construction of additional space for dedicated personnel locks and behind-the-barrier procedure rooms for the newly renovated housing areas.