It has previously been shown that Dendrostellera lessertii(Thymelaeaceae)has stronganticancer activity.In this study,the antileukemic activity of another new compound from the same plantextract is reported.Promyelocytic(NB4 and HL-60)and erythroleukemia(K562)cells were cultured in thepresence of various concentrations of the new compound(0.5-3.0 μtg/ml)for 3d.The cell numbers werethen determined by trypan blue exclusion test.The new compound inhibited growth and proliferation ofNB4,HL-60 and K562 with IC_(50) values of 1.5,2.0 and 2.5μg/ml,respectively.We also found that the newcompound inhibited cell proliferation in a dose-and time-dependent manner.At low concentrations and after48h of treatment,approximately 50%-70% of NB4 and HL-60 cells were differentiated to monocyte/macrophage lineage and approximately 30%-40% of the treated K562 cells were differentiated in the mega-karyocytic lineage,as evidenced by morphological changes and nitro blue tetrazolium reduction assays.Results of Hoechst 33258 staining also indicated that the new compound induced NB4 and HL-60 cellapoptosis at their respective IC_(50) values after 72h of treatment.Based on the present data,the new com-pound seems a good candidate for further evaluation as an effective chemotherapeutic agent acting throughinduction of differentiation and apoptosis. It has previously been shown that Dendrostellera lessertii (Thymelaeaceae) has stronganticancer activity. In this study, the antileukemic activity of another new compound from the same plantextract is reported. Promyelocytic (NB4 and HL-60) and erythroleukemia (K562) cells were cultured in thepresence of various concentrations of the new compound (0.5-3.0 μtg / ml) for 3d.The cell numbers were determined determined by trypan blue exclusion test. new compound inhibited growth and proliferation ofNB4, HL-60 and K562 with IC_ (50) values of 1.5, 2.0 and 2.5 μg / ml, respectively. We also found that the newcompound inhibited cell proliferation in a dose-and time-dependent manner. At low concentrations and after 48h of treatment, approximately 50% -70% of NB4 and HL- 60 cells were differentiated to monocyte / macrophage lineage and approximately 30% -40% of the treated K562 cells were differentiated in the mega-karyocytic lineage, as evidenced by morphological changes and nitro blue tetrazolium reduction assays. Results of Hoechst 33258 staining also showed that the new compound induced NB4 and HL-60 cellapoptosis at their respective IC 50 values ​​after 72 h of treatment. Based on the present data, the new com-pound seems a good candidate for further evaluation as an effective chemotherapeutic agent acting through induction of differentiation and apoptosis.