Hematological abnormalities or derangements have been demonstrated in patients suffering form microcystins (MCs) in hemodialysis unit in Caruaru, Brazil, 1996. While experimental study on hematological effect of microcystins has been rare and the underlying mechanisms are still puzzling. In the present study, microcystins were repeatedly intraperitoneally injected with a dose of 6 mu g/kg/day in rabbits (Oryctolagus cuniculus) for 14 days, and the prolonged effects of extracted microcystins on hematotoxicology were investigated. Significant decreases were observed in the hematological indices red blood cell counts, hematocrit, hemoglobin, and platelet count, while an obvious anemia occurred in rabbits after 14-day exposure. Moreover, red blood cell volume distribution width, mean corpuscular volume, and mean corpuscular hemoglobin did not vary significantly, indicating that rabbits suffered from normocytic anemia. In bone marrow, on the 14th day after toxin exposure, the frequency of micronucleus increased significantly, and the viability of bone marrow cells decreased markedly compared with the control. Serum erythropoietin levels declined on the 7th and 14th day, which suggested that the ability to regulate differentiation and maturation of erythrocytes was impaired. These results indicate that repeated exposure of microcystins can result in normocyte anemia, and the bone marrow injures and the sharp decreases of erythropoietin levels were responsible for the anemia. (C) 2011 Wiley Periodicals, Inc. Environ Toxicol 26: 472-479, 2011.