The assessment of the potential usefulness of enzymes as animal feed additives or treatments requires an understanding not only of the effect an enzyme has on its target substrate but also on the digestibility of that substrate. In vivo digestibility studies are expensive, time consuming and often involve invasive procedures that necessitate premature slaughtering of experimental animals. Preliminary laboratory screening methods can be used to indicate potential beneficial treatments prior to undertaking animal trials. The objective of this study was to assess the effect of protease pre-treatment of four differently processed soyabean meals on the digestibility of protein using an in vitro digestibility of nitrogen (Boisen and Fernandez 1997) technique as a screening method. The assumption implicit in this objective was that, if protease pre-treatment did not improve in vitro digestibility, it was unlikely to improve in vivo digestibility.