Renal elimination of a number of cationic compounds is thought to be mediated by the organic cation transporter 2 (OCT2, SLC22A2), a drug uptake transporter expressed at the basolateral domain of renal tubular cells. Recently, the key efflux transporter for the secretion organic cations was identified as an electroneutral H(+)/organic cation exchanger termed the multidrug and toxin extrusion (MATE)-type transporter 1 (MATE1, SLC47A1). The key goals of this study were to assess the interplay between the renal cationic transporters OCT2 and MATE1 and the functional assessment of genetic variation in human MATE1. First, the ability of various agents to interact with OCT2- or MATE1-mediated transport was determined using a recombinant vaccinia expression system. We were able to identify several drugs in clinical use with a divergent inhibitory capacity for these transporters. Subsequently, we further assessed the effect of those compounds on the cellular accumulation of shared substrates using OCT2 and MATE1 double-transfected cells. Consistent with data obtained using single transporter transfected cells, compounds that exhibited preferential inhibition of MATE1 such as rapamycin and mitoxantrone induced significant cellular accumulation of cationic substrates. We next assessed the functional relevance of MATE1 genetic polymorphisms. Significant loss of transport activity for metformin and tetraethylammonium was noted for two nonsynonymous single nucleotide polymorphisms (SNPs), c.404T>C (p.159T>M) and c.1012G>A (p.338V>A). The c.404T>C was only seen in Asian subjects with an allele frequency of 1%, and the c.1012G>A SNP was much more common, especially among those of African descent. In conclusion, we show that coordinate function of MATE1 with OCT2 likely contributes to the vectorial renal elimination of organic cationic drugs and that altered activity of MATE1, whether by drugs or polymorphisms, should be considered as an important determinant of renal cationic drug elimination.