The electron attachment rate constant of HCl is measured ine‐beam‐excited mixtures of N2/HCl and Ar/H2/HCl, by observing the electron current decay after termination of ane‐beam pulse. The possible enhancement of attachment due to vibrational excitation of HCl undere‐beam pumping is studied, by performing measurements withe‐beam currents differing by a factor of 30. The consequences of the results for XeCl laser kinetics are discussed.