The atomic geometries, energetic stabilities and electronic properties of TM@Zr-12(Z) (TM = Y-Cd, Z = 0, +/- 1) clusters are investigated with density-functional theory and relativistic all-electron basis sets. Optimization calculations and frequency analyses show that all the 45 considered icosahedral geometries are stable. It is also found that the bond lengths, binding energies and the gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals of the clusters obviously change with the interstitial atoms. The adiabatic ionization potentials and electron affinities are also relationship with the interstitial atoms. The role of the interstitial atoms on stabilizing the Zr-12 cage is examined. (C) 2008 Elsevier B.V. All rights reserved.