The geometric and magnetic properties of the M@Pb-12 clusters (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni) are studied using the relativistic density-functional method. The geometric optimization shows that the ground states of these clusters are close to the I-h structure. The magnetism calculations demonstrate that the magnetic moments of M@Pb-12 vary from 1 mu(B) to 5 mu(B) by doping different transition-metal atoms into Pb-12 cage, therefore, they possess tunable magnetic properties and have potential utility in new nanomaterials. The electronic structure calculation shows that the Mn@Pb-12 has large energy gap and doping energy. Furthermore, of particular interesting is that its structure and energy gap remain unchanged with a strong external electric field up to 0.1 V/angstrom, thus, Mn@Pb-12 would be a good candidate as the building block with high magnetic moment for cluster assembly. (C) 2008 Elsevier B.V. All rights reserved.