Abstract : The Naval Aviator's Speech Discrimination Test (NASDT), formulated in 1964, is used by the Bureau of Medicine and Surgery to evaluate aviators who fail to meet the hearing standards for aviation. The nature of the test, which involves a listening task for high-level speech signals with a simulated aircraft noise background, requires a tape recorder and earphone configuration. Two similar systems of test presentation have been developed and are in current use at 18 Navy and Marine Corps installations. The devices produce the properly controlled test signals required for the NASDT and are easily operated by trained corpsmen. Additional information is presented to enable the user of either system to administer the test properly.