Chalcones have been identified as interesting compounds with cytotoxic and tumor reducing properties. In the present study, the biological activity of synthetic chalcones on myeloid leukemic cells was investigated. Human myeloid HL-60 leukemia cells were exposed to 1-20 micro M chemicals for 0-96h. The viability of the cells was measured using trypan blue dye exclusion method. 4,4'-Dihydroxy chalcone (RVC-588) was selected for further experiments to determine characteristics of cytotoxicity among other compounds. The data show that cell viability decreased after treatment and IC(50) value was approximately 2 micro M for RVC-588. Cell differentiation was analyzed with cytofluorometry by changes in expression of glicoprotein surface markers CD11b/Mac-1, CD11c and CD14 together with morphological analysis. A maximum level of expression changes was determined at 72h but these changes were not statistically significant to show the differentiation of HL-60 cells to mature myeloid and/or monocytoid cells. Apoptotic DNA degradation was evaluated and quantitated using sensitive enzyme-linked immunoabsorbant (ELISA) method. Using this technique, a maximum level of apoptosis 1.2-fold higher than control was observed in cultures exposed for 48h to 2 micro M RVC-588. The DNA ladder assay was subsequently used to determine DNA breaks qualitatively. After 24h, the cells exposed to 2 micro M RVC-588 was shown to have cytotoxic-late apoptotic ladder pattern compared to control cells. These data demonstrate that RVC-588 has a high cytotoxic and antitumor activity in HL-60 cells among other chemicals we synthesized. Although the mechanism by which RVC-588 initiated cell death in these cells is presently not known and apoptotic mechanisms are likely to play less role compared to other chalcone analogues reported previously.