The purpose of this study was to evaluate the pharmacokinetics of cyclosporine (Cy) in woodchucks (Marmota monax) and Pekin ducks. These data are needed to design rational dosing regimens. Pharmacokinetic parameters were calculated from blood concentration‐time data obtained following intravenous (i.v.) administration of 10 mg/kg body weight to woodchucks and Pekin ducks. Whole blood samples were collected in EDTA and assayed using a commercially available radioimmunoassay kit that employs a monoclonal antibody specific for Cy. The blood concentration‐time profile best Dtted an open, two‐compartmental model in Pekin ducks. Compartmental analysis of data in woodchucks did not adequately describe the data. When non‐compartmental pharmacokinetic analysis of the data was performed, the resulting mean (± SD) pharmacokinetic parameters in woodchucks and Pekin ducks, respectively, were as follows: volume of distribution at steady‐state, 2.9 (± 0.8) and 2.7 (± 0.2) L/kg; systemic clearance, 10.2 (± 2.8) and 28.6 (± 6.1) mL/kg/min; mean residence time, 4.8 (± 1.1) and 1.6 (± 0.3). These data suggest that Pekin ducks clear Cy at a faster rate than do woodchucks and that a greater dose of Cy should be administered to Pekin ducks in order to achieve adequate i