Changes in hormonal and haematological level were assessed in male wistar albino rats treated with methanolic extract of Parthenium hysterophorus L. The result showed that methanolic extract treatment caused a significant (p < 0.01) reduction of 20 % and 40% in total RBC count (6.25 ± 0.025 to 5 ± 0.5 x 106/µL) and haemoglobin (17.1 ± 0.1892 to 10.2 ± 0.79 g / dL) respectively in treated rats over control. Unlike haematological parameters, hormonal profile showed a significant increase of 40% (p < 0.05), 200% (p < 0.01), 100% (p < 0.01) and 45.08% (p < 0.001) in follicle stimulating hormone, leutinizing hormone, prolactin and testosterone respectively. The reduction of blood parameters is due to less haemopoiesis or induction of anemia. The increase in hormone level may be a cause of prostate cancer in wistar albino rats
