In previous work, we reported the development of the B9/BM1 syngeneic murine bone marrow metastasis model. Interleukin (IL)-6–dependent, IL-1–producing B9/BM1 cells, which preferentially home to and colonise the vertebral and femoral marrow after i.v. injection, exhibit striking similarity in cell surface phenotype to human myeloma cells, especially the expression of 3 adhesion molecules, CD44, VLA-4 and ICAM-I. Because the haematopoietic microenvironment consists of different cell types, such as endothelial cells, fibroblasts, adipo-cytes and macrophages, we investigated the functional significance of these adhesion molecules in heterotypic binding assays between B9/BM1 cells and a newly established bone marrow-derived endothelial cell line (BMEC), a fibroblastoid pre-adipocyte cell line (BMS2.2) and primary bone marrow-derived macrophages. B9/BM1 cells adhered well to all stromal elements: a combination of monoclonal antibodies (MAbs) against CD44 and VLA-4 significantly inhibited the adherence of B9/ BM1 cells to BMEC and BMS2.2 cells, whereas binding of B9/BM1 cells to macrophages was partially blocked with an anti-ICAM-I MAb. Our results implicate multiple recognition mechanisms, including those involving CD44, VLA-4 and ICAM-I, in the retention of B9/BM1 cells in the bone marrow. © 1995 Wiley-Liss, Inc.