The authors present a numerical study of localization properties on models for amorphous solids in three dimensions. Tight-binding Hamiltonians that are based on the diamond structure are used to describe the electronic structure of amorphous modifications of carbon, silicon and germanium. The localization behaviour of electronic states is calculated by studying the sensitivity of eigenvalues to a change in boundary conditions. A wide spectrum of localization effects can be observed, including electron localization both at the band edges and weak localization within the bands. The origin of electron localization is discussed using a population analysis of eigenfunctions.