Researchers at the University of Illinois determined the standardized total tract digestibility (STTD) of phosphorus in several palm kernel meals and soybean meal (SBM) without or with exogenous phytase. Pigs were housed individually in metabolism cages and allotted to 11 diets with 6 replicate pigs per diet in a generalized randomized block design. Five semi-purified diets were formulated by mixing cornstarch and sugar with the test protein. Five additional diets were formulated with 800 units of phytase. A phosphorus-free diet was also formulated to measure basal endogenous losses of phosphorus by the pigs. After a 5-day adaption period, feces were collected for 5 days. The soybean meal contained 0.67% total phosphorus and 0.44% phytate phosphorus. The addition of phytase increased (P< 0.05) the apparent total tract digestibility (ATTD) of phosphorus in the soybean meal from 41.1 to 72.2%. The STTD of phosphorus was also increased (P < 0.05) from 49.6 to 81.1% for the SBM when microbial phytase was added to the diet. This study showed that microbial phytase increased phosphorus digestibility of the palm kernel ingredients and the soybean meal when fed to growing pigs. In addition, they reported that the concentration of phytate phosphorus affects the response to microbial phytase.