Although fibrosis and gelatinous transformation of bone marrow stroma are well known, there have been few histopathological descriptions in the literature. We studied 16 cases of acute leukemia, and describe the myxomatous changes of bone marrow stroma observed at 2 or 3 weeks following chemotherapy. We analyzed the extracellular matrix components immunohistochemically, using monoclonal or polyclonal antibodies raised against collagens, proteoglycans (PG), fibronectin and laminin. We found that the major components of the myxomatous matrix were chondroitin 6-sulfate PG and large PG. The stainability resembles that of extracellular matrix components in long-term bone marrow culture. We suppose that the myxomatous matrix provides favorable conditions for hematopoiesis, because hematopoietic cells proliferate and differentiate as soon as such stromal changes occur.