The involvement of bone marrow in the pathology of experimental P. brasiliensis infection in BALB/c mice was investigated. The histopathological features of bone marrow induced by the fungus were correlated with hematological changes in peripheral blood from 1 to 28 days post-infection. Intense lymphopenia and moderate neutrophilia were detected. The early changes in bone marrow included (i) maturation arrest characterized by an increase in immature blood cell precursors, mainly of granulocytic origin, (ii) intense vascular congestion when compared with the vessels of normal marrow, and (iii) an increased number of megakaryocytes. The normal histological pattern of bone marrow was restored by 28 days post-infection. No histologically recognizable lesion, such as granuloma formation or an abnormal cellular infiltrate, which could indicate the presence of the P. brasiliensis in bone marrow, was observed. In addition, special stains were unable to detect the fungus. The mechanisms responsible for the alterations described here are still unclear but are probably related to more general phenomena affecting the host rather than to direct damage of the precursors cells by P. brasiliensis