The high-energy antimatter telescope (HEAT) instrument has been flown successfully by high-altitude balloon in 1994 and 1995, in a configuration optimized for the detection and identification of cosmic-ray electrons and positrons at energies from about 1 GeV up to 50 GeV and beyond. It consists of a two-coil superconducting magnet and a precision drift-tube tracking hodoscope, complemented with a time-of-flight system, a transition radiation detector and an electromagnetic shower counter. We review the design criteria for optimal e+/- detection and identification, and assess the instruments' performance and background rejection during its first two flights. We also review the adaptation of HEAT for measurements of high-energy cosmic- ray antiprotons and for isotopic composition studies.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.