We investigate the concentration and short-range order dependence of the zero-temperature resistivity and thermopower for substitutionally disordered alloys from a first-principles approach. The alloy disorder is simulated by calculating the electronic structure of a large supercell (typically 200–250 atoms) with periodic boundary conditions. For the strong-scattering alloys we consider, the electron mean-free path is much less than the supercell dimension, causing artificial effects of periodicity to be negligible. In spite of strong scattering, there is no evidence for localized states near EF. The resistivity and thermopower are averaged over several configurations resulting in statistical error bounds of approximately ±10%. The concentration-dependent resistivity of substitutional V1−xAlx alloys agree well with Korringa-Kohn-Rostoker coherent potential approximation (KKR CPA) calculations. This confirms the accuracy of KKR CPA theory.