The high-frequency optical constants of graphite are computed from electron energy loss results by using a dispersion relation for anisotropic materials. The values of ɛ⊥(ω) are in reasonable agreement with those obtained by Taft and Philipp from optical measurements. The values of ɛ‖(ω) connect with those previously obtained at lower frequency from reflectivity measurements, and show a structure with two absorption peaks at 11.2 eV and 16 eV and two plasmons at 14 eV and 19 eV. The results are explained in terms of interband transitions, using a two-dimensional band structure. The experimental peaks in the energy loss function are shown to be due both to plasmons and to a different kind of excitation. To understand the peak position in energy as a function of the direction of the momentum transfer, a noncrossing rule due to the interaction between these two excitations is required.