Electron correlation effects on nuclear spin-spin coupling tensors arising from core-valence interaction were investigated with ab initio calculations based on multiconfigurational self-consistent field (MCSCF) reference states, an adequate basis set, and large restricted active spaces. Calculations of first and second-row hydrides were performed to examine the effect of including the core and semicore orbitals in the active molecular orbital space. The effects of using a multireference wave function instead of a single-reference one, as well as different numbers of electrons in the virtual orbitals, were considered. In second-row hydrides, the inclusion of semicore orbitals is found to be necessary for accurate calculations of spin-spin couplings involving the heavy nucleus. A smaller but nonnegligible effect is observed also for the hydrogen-hydrogen coupling. Comparison is made with nuclear shielding and electric field gradient, for which the effect is considerably smaller. Recommendations for wave functions for calculations of spin-spin couplings are given. (C) 2001 American Institute of Physics.