A systematic study of the 2H quadrupole resonance spectra of KHCO3 by double resonance methods and their changes with deuteration ratio has shown that the two sets of signals observed arise from the bicarbonate ion dimers [HCO3 . DCO3]2– and [DCO3 . DCO3]2–. The 2H quadrupole coupling constants of these two species themselves increase with deuteration ratio, due largely to the lattice expansion. Their intensities can be explained in terms of a relatively simple model for the double resonance process. The anisotropy of the 2H electric field gradient tensor is compared with that of the 1H chemical shift tensor recently deduced from high-resolution studies of a single crystal, and it is shown that it is reasonable to expect the inequality in the axial components of the two tensors to be related.