The effect of γ-ray irradiation on a high-birefringence polarisation-holding fibre is investigated. A permanent attenuation of 2000 dB/km at a wavelength of 0.85 μm results from a dose of 6 × 105 rad. For the same dose, there is no appreciable change in either the fibre birefringence or the polarisation-holding parameter. This indicates that no significant crosscoupling of the polarisation modes is caused by the defects induced by ionising radiation.