Photofragmentation mass spectra of metal-fullerene clusters C60Mx and C70Mx (M={Fe, Co, Ni, Rh}; x=0,...,30) reveal the existence of a reaction channel which yields clusters having the composition C59-2nM and C69-2nM (n = 0,...,10). Enhanced abundances of clusters with 44, 50, and 60 atoms, as well as the presence of clusters containing almost exclusively an even number of atoms, indicate that one carbon atom of the fullerene cage is replaced by a transition metal atom. Additional tandem time-of-flight (TOF) experiments on mass selected C59M and C69M indicate that the initial fragmentation step of this new kind of substitutionally doped fullerenes is the loss of a neutral MC molecule. Measurements on preselected C70Rh3 and C70Ir2 were performed in order to monitor in detail their laser induced transformation into C69Rh and C6Ir.