Oxaliplatin (L-OHP), a diaminocyclohexane platinum derivative, is an active and well tolerated anticancer drug which is presently used in the treatment of gastrointestinal tumours. Since the efficacy of L-OHP in the treatment of multiple myeloma (MM) has not yet been evaluated, we studied the antiproliferative activity of this compound in vitro in a panel of MM cell lines (XG1, XG1a, U266 and IM-9). We found that L-OHP inhibited the growth of MM cells at therapeutically achievable concentrations (IC(50): 5-10 microM after 24 h of exposure) and was more active than Cisplatin (CDDP) or Carboplatin (CBDCA). The activity of L-OHP was apparently not affected by interleukin-6 (IL-6), the major growth and survival factor of MM cells. We also found that L-OHP induced apoptotic cell death. We demonstrated that the combination of L-OHP with Dexamethasone (Dex) resulted in the enhancement of the anti-myeloma effects. L-OHP and Dex both induced poly adenosine diphosphate (ADP)-ribose polymerase (PARP) cleavage and this induction was enhanced by the combined treatment. L-OHP-induced apoptosis correlated with caspase-3 cleavage, but this correlation could not be demonstrated in Dex-treated cells. Taken together, these in vitro results provide a rationale for the experimental use of L-OHP in the treatment of MM patients and suggest therapeutic combinations of potential value.