A new long-wavelength infrared test facility is being developed at Ames Research Center to conduct proof-of-performance tests of focal plane arrays for the Infrared Astronomical Satellite (IRAS) telescope. This facility is believed to be unique in that it will cali-brate full-sized arrays designed for the 5-120 µm region of the IR spectrum under simulated spaceflight conditions and at background levels as low as 8 x 106 photons/cm2 second. Most of the tests will be performed in a main test chamber which contains a liquid helium shroud, blackbody sources, an arrangement to simulate zodiacal background, and spot scanning optics. A noncontaminating high-vacuum pumping system will be used to evacuate the chamber prior to cool-down to prevent molecular deposition. All housekeeping and focal plane signal outputs are multiplexed, digitized, and transmitted on high-speed data lines to a PDP-11/70 computer. The computer provides real-time displays on a color CRT terminal and stores data for subsequent reduction and hard copy output. An overview of the conceptual design and performance specifications of the test facility are given.