The intersublattice relaxation rate is measured as a function of the temperature for the excitons arising from the 6 A 1 → 4 Ti(I) transition in MnF 2 . It is found that this rate is dominated by scattering with thermal magnons at temperatures above 10 K. The matrix element governing the magnon-induced intersublattice coupling is determined to be 0.086±0.006 cm -1 . The relaxation rate at lower temperatures amounts to (0.75±0.15)×10 6 s -1 , and is consistent with exchange coupling perturbed by the spin-orbit interaction. The low-temperature rate is found to increase by the addition of Zn 2+ impurities up to concentrations of order 1 at, %