The structures of monoclinic (C2/m) lithium dihydrogenphosphate, LiH2PO2, and tetragonal (P4(1)2(1)2) beryllium bis(dihydrogenphosphate), Be(H2PO2)(2), have been determined by single-crystal X-ray diffraction. The structures consist of layers of hypophosphite anions and metal cations in tetrahedral coordination by O atoms. Within the layers, the anions bridge four Li+ and two Be2+ cations, respectively. In LiH2PO2, the Li atom lies on a twofold axis and the H2PO2- anion has the PO2 atoms on a mirror plane. In Be(H2PO2)(2), the Be atom lies on a twofold axis and the H2PO2. anion is in a general position.