The W-Os, Re-W, Re-Mo, Re-Hf, and Mo-Hf binary systems were investigated for superconductivity down to 1°K. Several new superconducting regions were found with the most significant occurring in the primary and terminal solid-solution alloys. The occurrence of superconductivity in the β-phase field of the Re-Hf and Mo-Hf binaries indicates a possible explanation for the spurious superconducting effects sometimes observed in elemental hafnium.