The four-component formulation of the Dirac-Hartree-Fock (DHF) approximation is used to calculate the electronic g-tensors and nuclear hyperfine interaction A-tensors for a number of open-shell diatomic species. The four-component approach makes it possible to include all relativistic single-particle effects involving the calculated magnetic interactions within the spinor structure, using a compact computational formulation. Results for most of the molecules investigated here are in good agreement with experiment. (C) 2002 Published by Elsevier Science B.V.