Objective To investigate the effect of quercetin on PML gene and protein expression andlocalization in leukemia cell lines. Methods Cell morphology was assayed by Wright’s stain and fluorescence stain, and PML mRNA expression by RT-PCR , PML protein localization by immuno-fluorescence. Results NB4 and HL-60 cells differentiated morphologically after treatment with all-trans-retinoic acid (ATRA) while K562 cells did not differentiate. Typical apoptosis was found in each cell line after treatment with quercetin. Immuno-fluorescence analysis showed , after treatment with ATRA , the fusion protein disappeared in NB4 cells and PML protein relocated , while HL-60 and K562 cells had no difference from control cells. After treatment with quercetin, the fusion protein disappeared in NB4 cells, PML protein relocated, then degraded. In HL-60 cells and K562 cells, PML protein also located and then degraded . The expression of PML mRNA was not changed in all three cell lines after treatment with ATRA or quercetin. C Objective To investigate the effect of quercetin on PML gene and protein expression and localization in leukemia cell lines. Methods Cell morphology was assayed by Wright’s stain and fluorescence stain, and PML protein localization by immuno-fluorescence. Results NB4 and HL-60 cells differentiated morphologically after treatment with all-trans-retinoic acid (ATRA) while K562 cells did not differentiate. Typical apoptosis was found in each cell line after treatment with quercetin. Immuno-fluorescence analysis showed, after treatment with ATRA, the fusion protein disappeared in NB4 cells and PML protein relocated, while HL-60 and K562 cells had no difference from control cells. After treatment with quercetin, the fusion protein disappeared in NB4 cells, PML protein relocated, then degraded. PML protein also located and then degraded. The expression of PML mRNA was not changed in all three cell lines after treatment with AT RA or quercetin. C