The relativistic coupled-cluster method starts from the Dirac-Coulomb-Breit Hamiltonian in its low-frequency approximation and includes correlation by Fock-space coupled-cluster with single and double excitations. One- and two-component approximations using the-Douglas-Kroll transformation are also tested. Significant relativistic effects are found for CdH, with bond length contracting from 1.820 to 1.778 Angstrom (experimental 1.781 Angstrom) and binding energies decreasing from 0.87 to 0.70 eV (experimental 0.68 eV). The binding energy of the cation increases by 0.1 eV upon inclusion of relativity. The electron affinity of the molecule is 0.44 eV. The Douglas-Kroll values include nearly all the relativistic correction. (C) 1988 American Institute of Physics. [S0021-9606(98)01609-2].