MDC-9 is a widely expressed member of the metalloproteinase/disintegrin/cysteine-rich protein family. The disintegrin domain of MDC-9 lacks an RGD motif but has recently been reported to bind the alpha (6)beta (1) integrin; however, it is unclear whether MDC-9 can bind other integrins. In the present study myeloma cells, but not lymphoblastoid cells, were shown to bind to immobilised, recombinantly expressed MDC-9 disintegrin domain (A9dis). Binding was divalent cation-dependent, being supported by Mn2+ and Ca2+. Adhesion of myeloma cells to A9dis was completely inhibited by an antibody to the alpha (v)beta (5) integrin but not by antibodies to other subunits. RGD-containing peptides had no effect on binding, suggesting that MDC-9 interacts with alpha (v)beta (5) in an RGD-independent manner. Flow cytometric analyses demonstrated that myeloma cells, but not lymphoblastoid cells, expressed alpha (v)beta (5) On the cell membrane. These data indicated that the disintegrin domain of MDC-9 can function as an adhesion molecule by interacting with an alpha (v)beta (5) integrin.