Nonspecific chronic hepatitis and increased activities of serum aminotransferases have been reported in cetaceans (dolphins, porpoises, and whales). We identified bottlenose dolphins in our current population with episodic increases in serum aminotransferases, specifically alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and we hypothesized that hematologic and serum biochemical changes in these animals may provide clues as to potential causes of liver disease in cetaceans. A retrospective case-control study involving 1,288 blood samples collected during 1998-2006 from 18 dolphins (six cases and 12 age- and sex-matched healthy controls) was conducted to compare eosinophil and platelet counts; and serum proteins, albumin, globulins, bilirubin, gamma glutamyltransferase (GGT), cholesterol, triglycerides, glucose, iron, and erythrocyte sedimentation rates. Bottlenose dolphins with increased ALT and AST activities were more likely to have higher serum globulins, bilirubin, GGT, iron, glucose, triglycerides, and cholesterol levels, greater erythrocyte sedimentation rates, and lower platelet counts compared to healthy controls. Our findings suggest that dolphins with chronic increases in aminotransferases may have a chronic hepatitis involving iron overload with similar etiologies and pathophysiology compared to terrestrial mammals. Areas for future research include predisposing metabolic risk factors; associations between iron overload and a diabetes-like condition; and a potential overlap syndrome involving autoimmune responses that may or may not be associated with viral infection.