Interspecies variation in drug disposition can be considered to be a function of species body weight. Therefore, it is possible to establish allometric relationships between pharmacokinetic parameters and species body weight. Interspecies scaling of pharmacokinetic data yielded from laboratory animals can often provide reliable predictions of pharmacokinetic parameters and drug disposition in humans. Significant correlations between 3'-azido-3'-deoxythymidine (AZT) pharmacokinetic parameters (total clearance, renal clearance, nonrenal clearance and steady-state volume of distribution) from mice, rats, dogs, monkeys and humans and body weight were found. Plasma AZT concentration versus chronological time profiles were markedly different for each species. However, when chronological time was converted to pharmacokinetic (physiologic) time these profiles were superimposible. These results demonstrate that interspecies pharmacokinetic scaling can be used to estimate plasma AZT concentrations in humans and can be used to design initial dosage regimens.