[en] With few exceptions the WIMS library data have been unchanged since the 1960s and most of the validation of WIMS is based on datasets that were in existence at that time. The main aim of the present study was to re-assess the U235 thermal data. Other proposed data modifications include further adjustments to the U238 fast and resonance data, a correction to the Pu239 resonance integral and a consistent choice of fission spectrum. A variety of experiments from solid uranium metal to dilute solutions of U235, representative of the enormous range on which WIMS validation is based, have been analysed with the proposed data and the overall agreement is now generally very satisfactory. (U.K.)