Surface plasmons are hybrid modes of longitudinal electron oscillations and light fields at the interface of a metal and a dielectric1, 2. Driven by advances in nanofabrication, imaging and numerical methods3, 4, a wide range of plasmonic elements such as waveguides5, 6, Bragg mirrors7, beamsplitters8, optical modulators9 and surface plasmon detectors10 have recently been reported. For introducing dynamic functionality to plasmonics, the rapidly growing field of organic optoelectronics11 holds strong promise due to its ease of fabrication and integration opportunities. Here, we introduce an electrically switchable surface plasmon source based on an organic light-emitting diode. The source provides a freely propagating surface plasmon beam and is potentially useful for organic integrated photonic circuits and sensing applications. Furthermore, the demonstration of controlled coupling of surface plasmons and excitons in organic materials could prove useful for the fabrication of improved organic light-emitting diodes and organic photovoltaic devices.