The first astronomical detection of NH, the imidogen radical, was made by Swings et al., who observed and identified the molecule in comet Cunningham by means of seven lines in the ultraviolet due to electronic excitations. The comet was visible in late 1940 and early 1941. The observations were made at McDonald Observatory with a Cassegrain spectrograph. NH was also observed by Feldman et al. in comet Halley.

NH was not identified in the interstelllar medium until 1991, when Meyer & Roth observed it toward ζ Persei and HD 27778. In 1997, Crawford & Williams observed NH toward ζ Ophiuchi. NH was not detected in the ISM with rotational spectroscopy until 2010, when Persson et al. observed the J=1-0 transition toward W31C with Herschel/HIFI.