An estimation has been made of the minimum loss that might be expected in ZrF. based IR fibre taking into account extrinsic absorption losses as well as the intrinsic loss mechanisms associated with the IR edge and Rayleigh scattering. The results suggest that an overall loss of approximately 0.03 dB/ km might be expected at 2.56 μm, a factor of three higher than the intrinsic loss and a factor of seven lower than overall loss in a typical silica fibre.