The end product of human purine metabolism is urate, which is produced primarily in the liver and excreted by the kidney through a well-defined basolateral blood-to-cell uptake step. However, the apical cell-to-urine efflux mechanism is as yet unidentified. Here, we show that the renal apical organic anion efflux transporter human multidrug resistance protein 4 (MRP4), but not apical MRP2, mediates ATP-dependent urate transport via a positive cooperative mechanism (K_m of 1.5 ± 0.3 mM, V_max of 47 ± 7 pmol·mg⁻¹·min⁻¹, and Hill coefficient of 1.7 ± 0.2). In HEK293 cells overexpressing MRP4, intracellular urate levels were lower than in control cells. Urate inhibited methotrexate transport (IC₅₀ of 235 ± 8 μM) by MRP4, did not affect cAMP transport, whereas cGMP transport was stimulated. Urate shifted cGMP transport by MRP4 from positive cooperativity (K_m and V_max value of 180 ± 20 μM and 58 ± 4 pmol·mg⁻¹·min⁻¹, respectively, Hill coefficient of 1.4 ± 0.1) to single binding site kinetics (K_m and V_max value of 2.2 ± 0.9 mM and 280 ± 50 pmol·mg⁻¹·min⁻¹, respectively). Finally, MRP4 could transport urate simultaneously with cAMP or cGMP. We conclude that human MRP4 is a unidirectional efflux pump for urate with multiple allosteric substrate binding sites. We propose MRP4 as a candidate transporter for urinary urate excretion and suggest that MRP4 may also mediate hepatic export of urate into the circulation, because of its basolateral expression in the liver.