Endohedral clusters formed from the Zintl ions Pb102− and Pb122− are particularly stable and therefore suitable for the assembly of larger aggregates. We therefore investigate the formation of Mg-doped lead clusters in the gas phase, and demonstrate that a whole series of new molecular cage clusters of lead can be generated by encapsulation of magnesium. Mass spectrometry reveals that some of the cluster compounds, with one and two Mg atoms attached to the lead clusters, display large intensities compared to the pure lead clusters, which indicates that the compound clusters are particularly stable. The magnesium-doped lead-cluster assemblies were further analyzed within a molecular-beam electric deflection experiment. Almost vanishing permanent dipole moments for MgPb10–16 support the idea that a single Mg atom could be encapsulated within a highly symmetric lead cage, which results in structures with not only enhanced stability but also increased symmetry compared to the pure lead clusters PbN.