EB1089, a novel 1,25-dihydroxyvitamin D3 analogue, has been known to have potent antiproliferative properties in a variety of malignant cells both in vitro and in vivo. In the present study, we analysed the effect of EB1089 on NCI-H929 human myeloma cells. EB1089 inhibited cell growth of NCI-H929 and efficiently induced the G1 phase arrest of the cell cycle in a dose-dependent manner. We could also detect apoptosis in NCI-H929 cells exposed to EB1089 (1 x 10-7 M for 72 h) using the sub-G1 group of the cell cycle by FACS and annexin V binding assays. Induction of apoptosis by EB1089 was associated with down-regulation of the Bcl-2 protein without change of the Bax protein. Regarding caspase activity, which plays a crucial role in apoptosis, EB1089-treated NCI-H929 cells revealed an increased activity of caspase 3 protease accompanied by degradation of the PARP protein in a dose- and time-dependent manner. In addition, EB1089 caused the down-regulation of p44 extracellular signal-related kinase (ERK) activity and up-regulation of the p38 kinase activity during apoptosis of NCI-H929 cells. These results suggest that EB1089 inhibits growth of NCI-H929 cells via G1 cell cycle arrest as well as apoptosis by activating p38 kinase and suppressing ERK activity.