The murine malignant histiocytosis sarcoma virus (MHSV) is a replication-defective murine retrovirus which contains a ras-oncogen. Upon intravenous infection of normal adult NIH-mice a rapidly fatal systemic proliferation of transformed mononuclear phagocytes develops. We have investigated the involvement of other mature hematopoietic lineages and of hematopoietic stem cells during the course of the disease. The erythroid lineage is affected by a profound anemia which is temporarily accompanied by an increase of erythroid precursors in bone marrow and spleen and a final ablation of erythroid stem cells. A granulopenia occurs with a concurrent decrease of granulocytic precursors and stem cells. The platelets fall to very low levels early during the disease despite of an increase of megakaryocytes and megakaryocytic stem cells. Multipotential stem cells show temporarily a slight increase followed by an almost total terminal ablation. The results show that MHSV has distinct effects on other hematopoietic lineages apart from its transforming properties.