Recent reports link Kaposi sarcoma-associated herpesvirus (KSHV) infection of bone marrow cells to bone marrow failure and lymphoproliferative syndromes. The identity of the infected marrow cells, however, remains unclear. Other work has demonstrated that circulating mononuclear cells can harbor KSHV where its detection predicts the onset and severity of Kaposi sarcoma. In either setting, bone marrow precursors may serve as viral reservoirs. Since mesenchymal stem cells (MSCs) in human bone marrow regulate the differentiation and proliferation of adjacent hematopoietic precursors, we investigated their potential role in KSHV infection. Our results indicate that primary MSCs are susceptible to both cell-free and cell-associated KSHV in culture. Moreover, infection persisted within nearly half of the cells for up to 6 weeks. Thus, MSCs possess a clear capacity to support KSHV infection and warrant further exploration into their potential role in KSHV-related human disease. (Blood. 2004;104:2736-2738)