We investigated Boettger's screened nuclear potential approximation for the spin-orbit interaction (SNSO) in the context of the Douglas-Kroll approach to relativistic Kohn-Sham theory. We extended the approximation to second-order terms and evaluated it for various atomic and molecular properties (spin-orbit splittings, g-tensor shifts, bond lengths, vibrational frequencies and binding energies) and compared the SNSO results with those of a self-consistent relativistic treatment of the electron-electron (ee) interaction. The SNSO approximation is comparable in computational effort to the model based on the nuclear potential only, but delivers molecular results that agree well with those of the more exact ee treatment. (C) 2003 Elsevier B.V. All rights reserved.