Brain delivery of active anti-HIV compounds is important for successful treatment of the AIDS patient. As an initial step in predicting human brain drug concentrations, hybrid pharmacokinetic models were developed to characterize the disposition of anti-HIV nucleosides following parent and prodrug administrations in mice. Mouse data were obtained following intravenous administration of 3'-azido-2',3'-dideoxyuridine (AZddU or AZDU), 3'-azido-3'-deoxythymidine (AZT), and their dihydropyridine prodrugs (AZddU-DHP and AZT-DHP). Exponential equations were fitted to the serum concentration-time data for each species, including the pyridinium ion moieties, and subsequently used in differential mass balance equations describing the brain dynamics of each compound. Model parameters for the mass balance equations were estimated by various techniques, including the utilization of in vitro data. In general, model-predicted brain concentrations agreed with the observed data. Similar data in larger animals will permit scale-up of the current model to predict human brain drug concentrations.