We investigated the darkening of nine high OH- fibre types irradiated with 500 MeV electrons from the Linac Injector of LEP (LIL) at CERN. The transmission of Xe light was measured in situ in the 350-800 nm range. The induced attenuation at 450 nm is typically 1.52+/-0.15 dB/m for a 100 Mrad absorbed dose. Two-parameter fits for darkening and recovery are presented. After irradiation the tensile strength remains essentially unchanged. For Polymicro quartz core fibres the tensile strength is typically 4.6+/-0.4 GPa. (C) 2002 Elsevier Science B.V. All rights reserved.