Multidrug resistance remains a major obstacle in the effective treatment of metastatic breast cancer. One mechanism by which multidrug resistance is conferred is the decreased intracellular drug accumulation due to the upregulation of the ATP-binding cassette (ABC) transporters. We have previously demonstrated that jadomycins, polyketide-derived natural products produced by Streptomyces venezuelae ISP5230, inhibit the growth of the human breast ductal carcinoma cell lines T47D and MDA-MB-435. To expand our understanding of jadomycin pharmacology, the goal of the present study was to determine whether the function of ABC efflux transporters affects the anticancer activity of jadomycins to MCF7 breast cancer cells. Seven jadomycin analogs (DNV, B, L, SPhG, F, S, and T) effectively reduced the viability of MCF7 control and ABCB1-, ABCC1-, or ABCG2-overexpressing drug-resistant MCF7 breast cancer cells as measured by methyltetrazolium cell viability assays and lactate dehydrogenase cytotoxicity assays. The inhibition of ABCB1, ABCC1, or ABCG2 with verapamil, MK-571, or Ko-143, respectively, did not augment the cytotoxicity of jadomycins DNV, B, L, SPhG, F, S, or T in drug-resistant MCF7 cells. Furthermore, jadomycins B, L, SPhG, F, S, and T did not increase the intracellular accumulation of ABCB1, ABCC1, or ABCG2 fluorescent substrates in HEK-293 cells stably transfected with ABCB1, ABCC1, or ABCG2. We conclude that jadomycins B, L, SPhG, F, S, and T are effective agents in the eradication of MCF7 breast cancer cells grown in culture, and that their cytotoxicities are minimally affected by ABCB1, ABCC1, and ABCG2 efflux transporter function.