A DFT investigation of substitutionally doped fullerenes MC59 of second- and third-row transition metals shows that their stability increases toward the right-hand side of the d-block. Whereas the structural deviation from that of C-60 depends on the size of the metal atom, stability is governed by electronic properties of the transition metal atom. A range of MC59 compounds of group 6-8 metals are predicted to have sufficient stability for experimental observation.