Superoxide dismutase (SOD) activity was determined in the erythrocytes and leukocytes of 5 patients with Fanconi’s anemia (FA) and 1 with atypical Fanconi’s anemia without any hematological disorder. SOD activity was decreased in the blood cells of the patients with Fanconi’s anemia, but was normal in the atypical patient. The influence of SOD on the chromosome aberrations and hematological disorder in FA is discussed.