In many dilute transition-metal alloys impurity atoms produce virtual bound d states which lie above the host d band. The factors governing the widths of these virtual bound states are discussed and a numerical calculation of these widths due to other authors is analysed and interpreted in the light of this discussion. The results are then used to interpret qualitatively experimental data on the magnetic susceptibility of some concentrated Zr alloys. Photoemission studies of some alloys are also discussed.