The development of a PBPK for the whole body in which inhalation, exhalation, and metabolism in RT tissues can be simulated was described. As an example of the model's use, the results of several experiments in which rats and humans were exposed to styrene were simulated. The predicted results agreed with the empirical data. The present model results were also in agreement with the results of the model of Ramsey and Anderson (1984) which, unlike the present model, does not simulate inhalation and exhalation or explicitly model the URT and TB region. In addition to describing the development and simulation results of a PBPK model, a procedure was illustrated that used such models in combination with laboratory animal data to predict dose in humans.