The existence of a left-handed (LH) transmission band in a bulk composite metamaterial (CMM) around 100 GHz is demonstrated experimentally. The CMM consists of stacked planar glass layers on which periodic patterns of micron-scale metallic wires and split-ring resonators are fabricated. The LH nature of the CMM band is proved by comparing the transmission spectra of individual CMM components. Theoretical investigation of the CMM by transmission simulations and an inversion scheme for the retrieval of the effective permeability and permittivity functions supports the existence of LH behavior. © 2006 The American Physical Society.