A technique has been developed for producing high strength, low void reinforced polyimide composites. The state-of-the-art on high temperature reinforced plastics has been advanced considerably with this system, designated BPI-373. Areas investigated include development of a suitable prepreg, development of a composite fabrication process, and generation of design data on various systems. Reinforcements included in the study are E-glass and quartz fabrics, boron filaments, and graphite yarn. Mechanical property data on the above systems have been developed at temperatures of 500 and 600 F and are presented.