Electron double resonance-detected NMR (EDNMR) is introduced as a powerful technique to directly measure metal hyperfine interactions in the active sites of metalloproteins. Measurement of these quantities by electron nuclear double resonance is usually difficult because of fast relaxation times and large anisotropic (dipolar) hyperfine couplings. In EDNMR, electron paramagnetic resonance (EPR) 'forbidden' transitions are excited, which become EPR allowed to some extent because of the presence of a large dipolar hyperfine and possibly quadrupole interaction. The usefulness of EDNMR is demonstrated with measurements on Ni-61-enriched hydrogenase of D. vulgaris Miyazaki F in the Ni-B state.