ISO 30024:2009 specifies the determination of phytase activity in feed samples. The method does not distinguish between phytase added as a feed additive and endogenous phytase already present in the feed materials. The method cannot be used to evaluate or compare the in vivo efficacy of the phytase product. It is not a predictive method of the in vivo efficacy of phytases present on the market as they can develop different in vivo efficacy per unit of activity. The method is suitable and validated exclusively for the determination of phytase activity and exclusively in complete feeds.