The present study aimed to investigate the interaction of zalcitabine with human organic anion transporter 1 (hOATI) during renal excretion. Contribution of OAT1 to the renal transport of zalcitabine was examined using the transfected cell lines overexpressing the human organic anion transporter1 (CHO/hOAT1 cells). Zalcitabine exhibited the inhibition effect on the cellular uptake of [3H]-PAH in CHO/hOAT1 cells with an IC50 value of 1.23 mM. Furthermore, the cellular uptake of zalcitabine increased threefold with the enhancement of hOATI activity in CHO/hOAT1 cells, while it was significantly reduced in the presence of OAT1 inhibitors such as ketoprofen, naproxen, PAH and 6-carboxyfluorescein. Those results suggest that hOATI contributes at least in part to the cellular uptake of zalcitabine across the basolateral membrane of proximal tubular cells.