Large numbers of eccentrocytes (erythrocytes with hemoglobin contracted to one side of the cell) were seen on a stained blood smear from a Dachshund with compensated hemolytic anemia. The 7-kg dog had been given 325 mg of acetaminophen orally once daily for 6 weeks by the client, because the dog exhibited signs attributed to abdominal pain. More than half of the erythrocytes contained small Heinz bodies visualized after methyl violet staining. The methemoglobin content was 6.4% (normal less than 2%) when measured 16 hours after the last acetaminophen tablet was given. High serum alanin transaminase and alkaline phosphatase activities and hyperbilirubinuria were measured. All abnormal laboratory findings were attributable to acetaminophen-induced oxidative damage to erythrocytes and hepatocytes.