In the zwitterionic title compound, C(18)H(16)N(2)O(4), the dihedral angle between the planes of the benzene and indole rings is 26.38 (10)°. An intra-molecular N-H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, mol-ecules are linked through N-H⋯O, O-H⋯O and C-H⋯O hydrogen bonds into infinite chains propagating in [010].