Pigs were self-fed one of six dietary concentrations (.20, .30, .40, .50, .60, .70%) of available phosphorus (AP) from 13 to 70 pounds body weight. Dietary available phosphorus concentrations of at least .50, .40, and .40% were needed for pigs weighing 23, 43, and 63 pounds, respectively, to maximize daily body weight gains and gain:feed ratios. Based on these data, the dietary AP needs of 13- to 70-pound pigs experiencing a moderate level of antigen exposure are 1.25 to 1.5 times greater than current NRC (1) estimates for similar weight pigs.