A study of lung function in microgravity, on the SpaceLab Life Sciences 1 mission will provide unique data. It should provide new insights into effects of normal gravitation on human lung fuction. It should also provide good information as to the effects of microgravity induced fluid shifts on the lung, and the extent of lung volume reduction that is predictable from the known effects of gravity on thoracic shape. The recent observation of reduced blood oxygen content in cosmonauts makes this new study especially timely. There is a constant risk of injury to the lung in space vehicles, from depressurization, and the inhalation of gases, vapors, and aerosols. Measurement of lung function in space crews has been delayed for decades. It is scheduled to occur, with increasing frequency, as plans for long duration missions advance.