The lower states of the PdH molecule have been studied with different relativistic methods. At the spin-free level, relativistic effects are shown to be crucial for a proper description of the molecule. PdH is shown to be a single-configuration molecule, but the configuration interaction (CI) results are highly sensitive to the choice of orbital basis, Spin-orbit interaction has been included through spin-orbit CI theory based on the second order Douglas-Kroll operator and through fully relativistic CI calculations based on the Dirac-Coulomb Hamiltonian. The results are in good agreement, but requires a proper choice of orbital basis in the spin-orbit CI calculation to ensure a balanced description of all Delta Sigma states coupled by spin-orbit interaction. (C) 1997 American Institute of Physics.