Knowledge of the disposition of macrolides in a single animal species has been insufficient for the prediction of the pharmacokinetics of macrolides in humans. To better understand the species differences in the pharmacokinetics of macrolide antibiotics, the disposition of erythromycin, oleandomycin, and tylosin in several mammalian species was examined. Generally, the serum concentration versus time profiles of these drugs after intravenous administration were described by two-compartment kinetic models and were similar within each species. These drugs were rapidly cleared, resulting in terminal half-lives of less than 2 h. Comparison of their pharmacokinetics showed greater variation in antibiotic disposition among animal species than noted for the differences within a species. When the pharmacokinetic data was fitted to an allometric model, the logarithms of volume of distribution, clearance, and half-life were linearly related to the logarithms of body weight. From these relationships, the human pharmacokinetics of erythromycin and oleandomycin were extrapolated and found to approximate observed human pharmacokinetics.