Reference range clinical serum chemistry values were established for free-ranging lactating northern fur seals (Callorhinus ursinus). Fur seals sampled for this study were part of a healthy and growing population in the Kuril Islands of far-east Russia. Blood was collected from 45 females between June and August 2005 to 2007. Fresh serum was assayed for 16 components. Packed-cell volume was determined from fresh whole blood. Results are made available for future comparisons with the declining population of northern fur seals on the Pribilof Islands and are compared with published values for other otariid species.