Corn contains approximately 0.26% phosphorus, but most of this phosphorus is bound to phytic acid, or phytate, and thus is not bioavailable to pigs because they lack the enzyme phytase. Corn-based diets can be supplemented with inorganic phosphorus to help meet pigs' phosphorus needs; however, rising costs of inorganic phosphorus makes this approach increasingly uneconomical. Helping pigs digest more of the phosphorus that naturally occurs in the diet could provide a cost-effective alternative to inorganic phosphorus supplementation while also helping to reduce the environmental burden of excreted phosphorus. An experiment was conducted to determine how adding graded levels of microbial phytase affected the standardized total tract digestibility (STTD) of phosphorus in corn and corn co-products. From these data, regression equations were developed to predict the response to adding different levels of phytase to each ingredient.