The title compounds, (C(8)H(20)N)[H(2)AsO(4)][H(3)AsO(4)](2), (I), and (C(6)H(14)N(2))[H(2)AsO(4)](2)[H(3)AsO(4)], (II), are unusual salts containing organic cations, dihydrogenarsenate anions and neutral arsenic acid molecules. In (I), the dihydrogenarsenate anion lies across a twofold rotation axis in the space group C2/c, while the cation is disordered across a centre of inversion. The [H(2)AsO(4)](-) and H(3)AsO(4) species interact by way of O-H...O hydrogen bonds, leading to sheets and a three-dimensional network for (I) and (II), respectively.