The effects of antimetabolites on the growing dynamics of human bone marrow stromal cells and their support of hemopoietic cells were tested by using a modified version of Dexter's culture system. Cytosine arabinoside (ara-C) was found to suppress neither the growing dynamics nor the supportability. On the other hand, methotrexate (MTX) suppressed the supportiveness, even though it hardly suppressed the growing dynamics. The recognition of injury to marrow cells could be of potential importance in cancer chemotherapy. Our in vitro evidence may provide clinical insights for cancer chemotherapy including prolonged marrow suppression or pretreatment of bone marrow transplantation.