Aim To explore the reversal of MDR(multidrug resistance) by nemadectin and milbemycin β1 from the milbemycin family to adriamycin-resistant human breast carcinoma cells(MCF-7 / adr). Methods MTT assay was used to evaluate the cell suppression rates and reversal effects. Intracellular accumulation of adriamycin was determined by HPLC. The accumulation of rhodamine 123(Rh123) was measured with spectrofluorometer. The expressions of P-gp and the MDR1 gene encoding P-gp were tested by flow cytometry and reverse...