The W(001) and Mo(001) surfaces are investigated by inverse photoemission. At Γ̄ we observe an unoccupied surface state just above the Fermi level. The angular dependence and chemisorption behavior identify it as a dz2 surface state similar to one observed and calculated just below EF. For W(001) a second state is seen near M̄ at 1.4 eV above EF and assigned to a ̄2 backbonding state. The implications of our data on the driving mechanism for the surface reconstruction are discussed using all-electron self-consistent local-density calculations. © 1986 The American Physical Society.