<p><b>OBJECTIVE</b>To investigate the effects of curcumin (Cur) and erythromycin (EM) on multidrug resistance (MDR) reversal of K562/A02 cell line and their mechanism.</p><p><b>METHODS</b>MTT assay was employed to determine the sensitivity of Cur, EM-treated K562/A02 cells to adriamycin (ADM). Flow cytometry was used to measure intracellular mean fluorescence intensity (MFI) of daunorubicin (DNR). P-gp expression was determined by immunohistochemistry. RT-PCR technique was used to examine the mdr1 mRNA level.</p><p><b>RESULTS</b>IC(50) of ADM in K562/A02 cells was decreased when treated with Cur or EM, and the reversal times (RvT) was 4.9, 3.7 respectively. The RvT reached to 11.3 when treated with Cur (2.5 microg/ml) combined with EM (120 microg/ml). The DNR MFI in K562/A02 cells was significantly lower than that in K562 cells (P < 0.01), and was increased significantly when treated with Cur (2.5 microg/ml) or EM (120 microg/ml) (P < 0.05). There was no significant difference between DNR MFI of K562/A02 cells treated with Cur (2.5 microg/ml) or EM (120 microg/ml). Immunohistochemistry showed that P-gp expression was significantly higher in K562/A02 cells than in K562 cells (P < 0.01), and was reduced in K562/A02 cells treated with each (P < 0.01), though being still higher than that in K562 cells (P < 0.01). P-gp expression of K562/A02 cells treated with each drug for 5 days were lower than that for 3 days (P < 0.01), and lowered further when treated with Cur and EM together (P < 0.01). Mdr1 mRNA level in K562/A02 cells was higher than in K562 cells (P < 0.01), and was decreased when treated with each of the drugs (P < 0.01). The mdr1 mRNA level of K562/A02 cells treated with Cur (2.5 microg/ml) plus EM (120 microg/ml) was decreased most significantly than that treated with other group of drugs. After 5 day treatment the mdr1 mRNA level of K562/A02 cells with Cur (2.5 microg/ml) was lower than that with EM 120 microg/ml (P < 0.01).</p><p><b>CONCLUSIONS</b>Either Cur or EM can partly reverse the multidrug resistance of K562/A02 cells and decrease the expression and function of P-gp in a time-dependent way. MDR reversing effect of Cur combined with EM is stronger than that of Cur or EM alone.</p>