An investigation of magneto-optic effects in gadolinium metal is reported. Samples prepared by vacuum evaporation were studied in situ under ultra-high-vacuum conditions to ensure clean optical surfaces. Magneto-optic Kerr rotation and ellipticity, determined using a null-type ellipsometric method, are used to calculate the magnetic contribution to the conductivity tensor. Data cover the 1-5-eV range at several temperatures. A simple model based on band calculations is used as a basis for interpretation of the data. The magneto-optic absorption is shown to have an intraband component and an interband component in analogy with ordinary optical absorption. A phenomenological intraband theory of the magneto-optic Kerr effect is presented and used to subtract out the intraband contribution from experimental data. Structure observed in the interband magneto-optic contribution to the conductivity is discussed in terms of $p\ensuremath{\rightarrow}d$ and $d\ensuremath{\rightarrow}f$ transitions. Numerical estimates of the signs and weights of these transitions are made in order to support this interpretation. A number of experimentally determined parameters associated with the band structure of Gd result from this work including $d$ bandwidth and general shape, location of unoccupied $4f$ states above the Fermi level, and the amount of "$p$ character" in occupied bands. It is found that the unoccupied $d$ bands have sharper structure and only qualitative agreement in the placement of the peaks compared to band calculations. The unoccupied $4f$ states are at a higher energy than predicted by calculations.