Selected hydrolytic enzymes are added to animal feeds in order to degrade specific antinutritional factors and(or) to increase availability of certain components of feedstuffs to the animal. A method is described that allows detection and quantification of beta-glucanase activity in complex feedstuffs. The method is based on radial diffusion of an enzyme-containing feed extract through an agar gel in which lichenan substrate (a relatively inexpensive glucan of mixed beta 1-->4 and beta 1-->3 linkages) has been dissolved. A linear relationship between the diameter of the zone of substrate hydrolyzed and the log of enzyme activity present was observed. The assay described is technically straightforward and requires no specialized equipment. At typical commercial inclusion levels (1 kg/t), the activity of a supplemental beta-glucanase, added to feed in a commercial mill was determined by averaging several measurements, with a precision of +/- 4%, variation between individual readings of +/- 11.3% (SD), and recovery of 109%. By using high-concentration feed extracts, the method was sensitive enough to detect background and(or) supplemental beta-glucanase activities as low as .05 kg/t supplement equivalent. This method allows consumers, producers, and regulatory authorities to measure the activity of beta-glucanase in feed at commercial inclusion levels and, hence, study the effects of processes such as pelleting and extrusion on such supplements.