This Method describes the determination of Ronozyme WX xylanase activity in feed samples The method does not distinguish between Ronozyme wx xylanase added as a feed additive and other xylanases (e.g. endogenous xylanase) already present in the feed materials The method cannot be used to evaluate or compare the in vivo efficacy of Ronozyme product. It is not a predictive method of the in vivo efficacy of xylanases present on the market as they can develop different in vivo efficacy per unit of activity obtained with the method described The method is suitable and validated exclusively for the determination of Ronozyme wx xylanase activity and exclusively in complete feeds 1 was developed on the basis of wx Therefore, it might necessarily be suitable as such for xylanase products presenty the might be developed in the future. The method is a tool which is useful only to evaluate the total Ronozyme WX activity in feed samples.