A linear combination of atomic orbitals (LCAO) of the Slater type is used in a variational treatment of the HeH2+ ion to achieve excellent results for the ground state energy of this heteronuclear diatomic system. As in our recent treatment of H, we use orbitals with identical screening constants but with increasing principal quantum numbers and angular momentum. This strategy was feasible because of our ability to accurately evaluate all overlap integrals. Unlike even tempered Gaussian-type LCAO, our results become more accurate at large interatomic separations. Using two different screening constants (one type associated with each atom) proved to be unnecessary. © 1993 John Wiley & Sons, Inc.