Periostin is a secreted protein that shares structural homology with the insect axon guidance protein fasciclin 1. Periostin is expressed predominantly in collagen-rich fibrous connective tissues that are subjected to constant mechanical stresses. We have shown previously that periostin is a novel component of subepithelial fibrosis in bronchial asthma. Here, we investigated the relationship between periostin and bone marrow (BM) fibrosis. Periostin was expressed in the stroma and stromal cells of BM fibrosis specimens and to a great extent its expression levels correlated closely to the grade of fibrosis, as estimated by silver staining. However, in the present study, we found no relationship between plasma periostin levels and the extent of BM fibrosis. We also demonstrated that periostin is secreted by human BM hTERT stromal cells and that its secretion is enhanced by TGF-beta, a cytokine produced by clonal proliferation of megakaryocytes and/or monocytes. These results indicate that periostin is a component of BM fibrosis and that it may play a role in the disease progression.