An electromagnetic stop band spanning about one octave is observed in a periodic structure consisting of a face-centered-cubic Bravais lattice of metal spheres supported by a low-loss dielectric. The low-frequency edge of the stop band is consistent with the Mie condition for the metallic spheres, and the center frequency of the stop band is a function of the lattice constant and the support dielectric material. For example, a sample having a cubic lattice constant of 1.65 cm, 3/8 in. diam chrome spheres at each atomic core, and Teflon support dielectric displayed a lower band edge of approximately 5.2 GHz, an upper band edge of about 12.8 GHz, and a maximum rejection at the center of the band of roughly 20 dB.