(±)-3-Carb-oxy-2-(imidazol-3-ium-1-yl)-propanoate.

The title compound, C(7)H(8)N(2)O(4), crystallizes as a zwitterion, with mol-ecules organized into mol-ecular sheets via carbox-yl-carboxyl-ate and N(+)-H⋯carboxyl-ate contacts. These sheets are constructed from translationally related mol-ecules that further link to neighboring motifs via π-stacking [centroid-centroid distance 3.504 (3) Å] and weak C-H⋯O contacts.