The Lunar-Mars Life Support Test Project (LMLSTP), formerly known as the Early Human Testing Initiative (EHTI), was established to perform the necessary research, technology development, integration, and verification of regenerative life support systems to provide safe, reliable, and self-sufficient human life support systems. Four advanced life support system test phases make up LMLSTP. Phase I of the test program demonstrated the use of plants to provide the atmosphere revitalization requirements of a single test subject for 15 days. The primary objective of the Phase II test was to demonstrate an integrated regenerative life support system capable of sustaining a human crew of four for 30 days in a closed chamber. The third test phase, known as Phase IIA, served as a demonstration of International Space Station (ISS) representative life support technology, supporting a human crew of four for 60 days. Phase III, the final phase, will integrate biological and physicochemical systems to support a crew of four for 90 days.The LMLSTP Phase II test was conducted June 12-July 12, 1996, in the Life Support Systems Integration Facility (LSSIF) at Johnson Space Center. The Phase II Atmosphere Revitalization System (ARS) maintained an acceptable atmosphere for the four-person test crew for the entire 30-day test. The ARS consisted of four primary subsystems. A Four-Bed Molecular Sieve (4BMS) Carton Dioxide Removal Subsystem removed carbon dioxide from the atmosphere. A Sabatier Carbon Dioxide Reduction Subsystem (CRS) reacted the carbon dioxide collected by the 4BMS with hydrogen to produce methane and water. A Solid Polymer Electrolyte Oxygen Generation Subsystem (OGS) electrolyzed water from the CRS and the Water Recovery System into hydrogen, which was used for carbon dioxide reduction by the CRS, and oxygen, which was used by the test subjects. An activated charcoal canister assembly was used for trace gas removal. This paper will describe the Phase II ARS in more detail, and discuss performance of the system during the 30-day test.