Phosphorus is the second most plentiful mineral in the animal body. It is present as structural component and it is involved in a wide variety of biochemical reactions. Research has been conducted in Brazil to study phosphorus metabolism in pigs using the model of Fernandez modified by Lopes et al. (2001). However there is little published information related to phosphorus metabolism in pigs using the model of Vitti et al. (2000). In the present study, it was considered the hypothesis that P intake regulates P utilisation and flow on gut, blood, soft tissues and bone. The isotopic technique by using labelled P allows the formulation of model of the biological flow of phosphorus in the animal organism. The aim of this study is to evaluate the effects of phosphorus intake on phosphorus metabolism in pigs, by using isotope and balance techniques. A mathematical model for phosphorus metabolism is formulated.