The intermolecular band dispersion related to the highest occupied molecular orbital in highly ordered, hydrated multilayer films of the DNA base guanine has been measured using photon-energy-dependent ultraviolet photoelectron spectroscopy. A bandwidth of 331 +/- 8 meV at room temperature and a small effective mass of about 1.11 times that of a free charge suggest a high intrinsic hole mobility along quasi-one-dimensional stacks formed perpendicular to layered, hydrogen-bound networks.