An HCl laser that uses isotopic V‐V energy transfer collisions as a pumping mechanism has been demonstrated. This multiline laser, which utilized an intracavity cold gas isotope filter, increased the energy from theP1lines of H37Cl while decreasing the energies of theP1andP2lines of H35Cl. Previously unreported lines, including emission fromR‐branch transitions, have also been observed from single‐line HCl and HBr lasers.