This paper presents a summary of the results of the last known closed-door manned chamber test of an operational regenerative life-support system. This is the 20th anniversary of the 90-day run performed in the McDonnell Douglas Astronautics Co. (MDAC) Space Station Simulator for the NASA Langley Research Center in the summer of 1970. Overall, 45 different organizations participated in the program. The life-support systems representative of those required by Space Station were installed within a double-walled chamber and operated by a four-man crew. Crew repair, maintenance, and operational performance for the life-support systems were evaluated. The 90-day test included the evaluation of a number of advanced life-support subsystems with backup provided by alternate subsystems that had undergone extensive manned testing during the middle 1960s. Data was obtained on the performance of the equipment, the four-man crew, and the man/system interface. The results of the testing were used to improve equipment designs for Skylab and the Space Station, and to increase our degree of understanding of the design impacts of closing the water and oxygen cycles. Significant results included (1) no psychological or physiological effects were encountered by the confined crew, who used the water and oxygen recovered, and (2) there was time to troubleshoot and repair equipment that malfunctioned.