VOIDS in metals, formed as a result of neutron irradiation or particle bombardments, are usually found to be distributed randomly in the lattice. But I have found that voids can take up regular positions in the lattice with respect to each other and demonstrate that the voids form a body-centred-cubic superlattice structure with crystallographic axes identical with those of the molybdenum matrix. The voids in this case were formed as a result of particle irradiations but some observations made on neutron irradiated molybdenum (F. W. Wiffen, private communication) indicate strongly that this same void structure may be present in that case as well.