The orthogonalized plane wave method, in a perturbation approximation, is used to compute the lowest lying conduction states in (fcc) solid argon at the symmetry points GAMMA , X, L, and K. The 3s and 3p valence bands are treated by tight-binding theory. The potential used in the computation consists of a sum of effective atomic potentials in which a free-electron-like expression is used for the exchange contribution, The lowest conduction state appears to be s-like ( GAMMA /sub 1), lying 12.4 ev above the highest valence state ( GAMMA /sub 15). The results of the computation are compared with theoretical and experimental knowledge of the electronic structure of the solid rare gases, (auth)