A systematic approach to the estimation of bioavailability using both model-independent and pharmacokinetic techniques is introduced. The methods of Kwan-Till and Wagner-Nelson or Loo-Riegelman are integrated such that one is able to check many of the assumptions inherent in these techniques and make appropriate adjustments for apparent deviations. The proposed integrated method makes use of all available data (both plasma and urine) and leads to a better understanding of the absorption, distribution, metabolism, and excretion of the drug being studied.