[en] The effect of successive deuterium substitution on the nitrogen-14 nuclear shielding constant and ¹J(¹⁴N,H) in the ammonium ion has been measured. Each additional replacement of hydrogen by deuterium resulted in an approximately 0.30 ppm increase in the nitrogen shielding. This is less than half that previously reported for liquid ammonia and approximately twice that reported for methane. These observations can be qualitatively accounted for by the theoretical model of Jameson. A measurable secondary deuterium isotope effect of ¹J(¹⁴N,¹H) was observed: on going from NH⁺₄ to NHD⁺₃ , ¹J(¹⁴N,¹H) decreased by 0.15 +- 0.03 Hz. The primary isotope effect on ¹J(¹⁴N,H) is less than 0.2 Hz