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The evolutionarily ubiquitous multidrug and toxin efflux (MATE) proteins mediate anticancer and antibiotic resistance, while transporting toxins, ions and flavonoids in plants. MATEs of the model amoeba Dictyostelium discoideum have not been studied although sequences of its pair group with the two Homo sapiensMATEs. Ddmate1 and 2 are both transcribed, Ddmate2 more so, with peaks in vegetative and slug life-cycle stages. Ddmate1 was upregulated in response to a toxin, ethidium bromide, at the lowest concentration tested. Removing MATE function by inhibitor or mutation increased intracellular levels of various compounds, confirming these as efflux transporters. Plasma membrane localisation was revealed using a GFP-MATE1 reporter-line. MATE1 and MATE2 phenotypes indicated roles beyond detoxification: on Klebsiella lawns these mutants produced significantly smaller plaques than WT, and their axenic growth rates were also lower. The transporters’ impact on use of Dictyostelium for novel drug research was tested using flavonoids. LCMS and fluorescence-imaging revealed differential flavonoid uptake. Flavanones such as naringenin did not cross into cells, whereas flavonols localised to mitochondria and cytoplasm. Ddmate1 transcription was upregulated, however, in response to naringenin, which is known to reduce levels of kidney-disease protein PKD2 in both Dictyostelium and animal cells. Increased flavonol intracellular concentrations confirmed that efflux not import was impeded in MATE1 and MATE2, and kaempferol therefore further reduced MATE1-cells’ growth. These D. discoideum MATEs may usefully model the HsMATEs, aid understanding of flavonoids’ effects, and should be considered when using this model eukaryote to screen drugs.