The unoccupied electronic structure of potassium on Cu(111) is determined by angle-resolved inverse photoemission. The observed spectral features are assigned to unoccupied 4p and 3d states of potassium. For a complete monolayer an ordered (2×2) overlayer structure is formed. The dispersion of the K-induced states is determined and compared to a recent band-structure calculation for an isolated K monolayer. © 1990 The American Physical Society.