Electron-nuclear double resonance. A magnetic resonance technique involving exitation of both electron spins and nuclear spins. Two sources of radiation are used. One is a fixed source at microwave frequency, which partially saturates the electron spins. The other is a variable radiofrequency source, which excites the atomic nuclear spins. Excitation of the nuclear spins affects the electron spins by hyperfire coupling, increasing the relaxation time of the excited electron spins and increasing the signal strength. The technique, which is usually done at low temperatures, is used to investigate paramagnetic molecules. See also electron paramagnetic resonance.