The effects of ochratoxin A (5 mg/kg, intraperitoneal) on clotting time, hemoglobin, total count of red blood cells and white blood cells and differential count of white blood cells were studied in mice. This mycotoxin caused a significant decrease in the hemaglobin level and in the total count of red blood cells. Among white blood cells there was a significant increase in small lymphocytes and a significant fall in the count of neutrophils, basophils and monocytes in treated mice. The administration of ochratoxin A also prolonged the clotting time by more than 6-fold. © 1979.