TRAIL-induced cytotoxicity in 2 human primary glioblastoma cell lines by XTT assay demonstrated that ED 326. BT was moderately sensitive in a dose-dependent fashion, whereas ED 273b. BT was resistant (< 20% response)(Fig. 1A). The results were confirmed by Hoechst staining for apoptotic nuclear morphology. Furthermore, these 2 cell lines were incubated with cisplatin or VP 16 for 24 hours at concentrations ranging from 20.00 to 0.33 [mu] g/mL. The chemotherapeutic drugs alone induced only a limited cell kill of these 2 cell lines (Fig. 1, B and C). This finding was similar to the 25% and 0% apoptotic cell kill identified with 100 ng/mL of TRAIL alone in ED 326. BT and ED 273b. BT respectively. When cisplatin or VP 16 was applied in combination with a fixed concentration of TRAIL (100 ng/mL) to ED 326. BT and ED 273b. BT cell lines, different results were obtained (Fig. 1, B and C). Here, ED 326. BT with low expression of Bcl-x^ sub L^ showed a synergistic response to TRAIL and cisplatin or VP 16, whereas ED 273b. BT with high level of Bcl-x^ sub L^ did not. Moreover, XIAP was expressed to a similar degree in both cell lines irrespective of their sensitivity to TRAIL (Fig. 1D).