High efficiency electrophosphorescent light-emitting diodes (LEDs), with an emission peak at 600 nm, a luminance of 2200 cd m(-2), and good operational stability were fabricated from a conjugated copolymer doped with an iridium complex. The devices exhibited an external quantum efficiency of 1.5% and a luminous efficiency of 3 cd A(-1). These results demonstrate that electrophosphorescent devices with high brightness and operational stability can be produced in the form of polymer LEDs fabricated by processing the active materials from solution.