Our previous experiments have shown that methylglyoxal bis(cyclopentylamidinohydrazone) (MGBCP), a polyamine synthesis inhibitor, suppresses the growth of osteosarcoma cells repressing their intracellular polyamine levels, and that this inhibition of cell growth is only partially reversed by the addition of polyamines. In the present study, we found evidence indicating that the incomplete recovery of cell growth by the addition of polyamines to the polyamine-depleted cells was due to programmed cell death (apoptosis) induced by MGBCP. Morphological changes showing blebbing and chromatin condensation were observed in MGBCP-treated cells, and hypodiploid subpopulations containing apoptotic cells were clearly visible in the profile of flow cytometric analysis. Characteristic oligonucleosomal-sized fragments were increased as the concentration of MGBCP was increased. The results presented here suggest that in addition to reducing the growth rates, MGBCP can induce apoptotic cell death in three human osteosarcoma cell lines.