Treatment with steroid is necessary for adult human bone marrow-derived stroma to support hemopoiesis in vitro. We have investigated the effect of the steroid methylprednisolone on the glycosaminoglycans produced by adult bone marrow stroma. Methylprednisolone did not significantly alter the amount of sulfated glycosaminoglycans produced but the amount of the nonsulfated glycosaminoglycan, hyaluronic acid (HA), was dramatically decreased by the steroid. Culturing methylprednisolone-treated stroma with exogenous HA reduced the proportion of sulfated glycosaminoglycans incorporated into the cell layer and increased the proportion secreted into the medium. It also reduced the capacity of the stroma to bind and stimulate blast colony-forming cells. In fetal liver stroma, methylprednisolone did not decrease the amount of HA or alter the type of heparan sulfate produced. Thus, the ability of stroma cells to respond to steroid and the amount of HA in the extracellular matrix may vary in different marrow microenvironments. This may have functional consequences regarding their abilities to support hemopoiesis.