The title compound NH(4) (+)·C(5)H(4)N(3)O(2) (-) crystallizes with two formula units in the asymmetric unit. In each anion, the carboxyl-ate is deprotonated and the planar amino group [angle sums of 359 (3) and 355 (3)° at N] remains protonated. In the crystal, the cations and anions are bridged by N-H⋯O and N-H⋯N hydrogen bonds, forming a three-dimensional network.