Venom toxins have been tested as anti-thrombotic, and anti-metastatic drugs in experimental models. The jararhagin toxin, from Bothrops jararaca snake venom, acts upon several biological processes, as inflammation, pain, platelet aggregation, etc. In this article, the systemic effects of intra-peritoneal injections of different jararhagin doses were determined in mice. About 50% significant decrease was observed in total blood leukocytes in the first (48 ng), and second (24 ng) weeks. The reduction of lymphocytes, monocytes and neutrophils accounted for this leucopoenia up to the sixth week. Significant increase in red blood cells was observed, especially on the third and fourth weeks (6 and 12 ng). A significant reduction in leukocyte infiltration was found in peritoneum (6, 12, 48 ng), whereas the infiltration was significantly increased in bronchial alveolar exudates (6 and 12 ng). The differential analysis of bone marrow cells showed significant increase, particularly of myelocytes (12 and 24 ng). These results show, at low doses, the toxin jararhagin induces red blood cells production, which is compensating the reduction of different leukocyte types. This severe leucopoenia suggests the occurrence of anti-proliferate activity or direct citotoxicity of jararhagin in the differentiation level of myeloid, and lymphoid stem precursor cells.