Objective: To investigate the inhibitory effect of combined administration bisdemethoxy curcumin (Bdmc) and adriamycin(ADR) on multidrug resistance HL-60/ADR cells. Method: HL-60/ADR cells were simultaneously treated with Bdmc within concentrations (1

2

4

8 μmol·L-1) and ADR(0.4

0.8

1.6

3.2 μmol·L-1)48 h respectively

the cell density was 2×104/hole. The inhibitory effect of both drugs on HL-60/ADR cells in vitro was evaluated by MTT. Cells were reated sequentially administration Bdmc(6

12

24

48 μmol·L-1) and ADR(0.08

0.2

0.4

1.0 μmol·L-1). The Jin's formula was used to analyze the the inhibitory effect. Result: The inhibition is 6.9%

11.8% when treated only with ADR(0.4

0.8 μmol·L-1)

while simultaneously treated with Bdmc(8 μmol·L-1) it was over 94%.In simultaneous administration Bdmc (1-8 μmol·L-1) combined with ADR(0.8-3.2 μmol·L-1) revealed a simple addition or potentiation effect. In addition

sequential administration of Bdmc followed by ADR had a synergistic effect;in contrast

sequential administration of ADR followed by Bdmc exhibited an antagonistic effect. Conclusion: Simultaneous administration of Bdmc and ADR reveals a synergistic effect and sequential administration of Bdmc and ADR exhibits an unidirectional synergistic effect.