A Human Metabolic Simulator (HMS) was developed for use in testing life support air revitalization systems. The developed equipment simulates atmospheric effects of human respiration, perspiration, and metabolism, including consumption of oxygen and production of carbon dioxide, water vapor, and sensible heat. By analogy with human metabolism, oxygen is converted into carbon dioxide and water vapor through catalytic oxidation (combustion) of an organic fuel. Virtually complete combustion of methyl acetate and ethanol fuels was demonstrated using a monolithic precious-metal catalyst at reaction temperatures above 275°C. The HMS has been used successfully in support of NASA's Early Human Testing (EHT) program.