A method is described which permits detection of 3h JNC′ scalar couplings across hydrogen bonds in larger, perdeuterated proteins. The experiment is demonstrated for the uniformly 2 H/13C/15N-enriched 30 kDa ribosome inactivating protein MAP30. The 3h JNC′ interactions are smaller than 1 Hz, but their detection in an HNCO experiment is made possible through the use of constructive interference between the 15N chemical shift anisotropy and 1 H-15N dipole-dipole relaxation mechanisms in a manner similar to that of recently proposed TROSY schemes. Sensitivity of the HNCO experiment depends strongly on the 15 N transverse relaxation rate of the downfield 15 N multiplet component and on the amide proton T1. In perdeuterated MAP30 at 40 °C, the average TROSY T2 was 169 ms at 750 MHz 1 H frequency, and a wide range of longitudinal relaxation rates was observed for the amide protons.