To calculate the neutron kinetic energy release parameters (kerma factors) for an element consisting of several isotopes, it is necessary to use separate neutron cross-section and radioactive decay data for each isotope. In the case of chlorine, cross sections for natural chlorine are available, but cross sections for the individual isotopes are not. Kerma factors for chlorine were calculated using natural chlorine cross sections and weighting the contribution of each isotope to the decay data, using the fractional contribution as a variable parameter. The kerma factors calculated at particular neutron energies are found to be sensitive to this parameter and dependent on that energy. The purpose of this Note is to encourage experimental determination of the relevant neutron cross sections of isotopically pure samples of chlorine.