Phosphorus is one of the most expensive nutrients in swine diets. Use of standardized total tract digestibility (STTD) of P, instead of apparent total tract digestibility (ATTD), may reduce the cost of diets because STTD values, unlike ATTD values, are additive in mixed diets. Values for STTD of P can be determined by correcting ATTD of P for the basal endogenous loss of P. The basal endogenous loss of P is estimated by using a P-free diet. Gelatin has been widely used in P-free diets because it does not contain any P and is a good source of protein. However, gelatin products can make diets dusty and sticky which can reduce the palatability of these diets and make them hard to work with. In addition, feeding pigs with diets containing no P may cause health issues in pigs. Blood plasma, casein, and potato protein concentrate are possible protein alternatives to gelatin because the P in blood plasma and casein is close to 100% digestible and potato protein concentrate provides very little P. Therefore, the objective of this experiment was to test the hypothesis that the basal endogenous loss of P from pigs fed a diet containing blood plasma, casein, or potato protein concentrate are not different from that of pigs fed a diet containing gelatin.