Blood meal and spray dried plasma protein are often included in diets fed to weanling pigs, and blood products are considered excellent sources of protein. The objective of this research was to measure apparent total tract digestibility (ATTD) and standardized total tract digestibililty (STTD) of phosphorus in spray dried animal plasma, porcine blood meal, and avian blood meal fed to weanling pigs. References such as the NRC typically provide relative bioavailability values for phosphorus rather than digestibility values. Relative bioavailability values, however, depend on the standard (e.g., monosodium phosphate or dicalcium phosphate) to which the availability is compared. Thus, these values are believed not to be additive in mixed diets. It is believed that STTD values are additive in mixed diets, and therefore will enable producers to formulate diets that accurately meet the phosphorus requirement of pigs without creating unneccesary excesses that are excreted in the manure.