Several morphologic studies have suggested that gap junctions exist between bone marrow stromal cells. This possibility was examined by analysis of stromal cells present in the adherent layer of primary long- term lymphoid bone marrow cultures and in additional studies using a stromal cell line. Results showing that the fluorescent dye lucifer yellow, when microinjected into a single stromal cell, transferred between most other contacting stroma and that stromal cells were electronically coupled provided support that cell-cell communication occurs between these microenvironmental elements. Additional studies showed that transcripts for connexin (Cx) 43, but not for Cx26 or Cx32, were present in a stromal cell line. To examine the potential for regulated cell-cell communication between the stroma, cells were treated with interleukin-1 (IL-1), a cytokine known to affect stromal cell function, and the effects on dye transfer were examined. IL-1 treatment resulted in a reversible decrease in the ability of dye to transfer between stromal cells in contact. Taken together, these studies show that gap junctions exist between stromal cells and that their permeability can be regulated. However, gap junction-mediated cell-cell communication could not be shown between the stroma and developing lymphoid cells.