This review deals with the different transport mechanisms mediating the apical and basolateral transport of organic anions, all of which are restricted to the proximal tubule. Several transport mechanisms, such as the para-aminohippurate basolateral transporter and the apical proton coupled di- and tripeptide transporter have been cloned, and their role in renal transport has been well characterized. Other transport proteins have been cloned from the kidney, liver, or intestine, but their role in the renal transport of organic anions needs to be elucidated. This is the case with Mdr2, oatp1 and OAT-K1, which were identified in the apical membrane of the proximal tubule, and with MDR1, the precise localization of which is still uncertain. Other apical transport mechanisms, sodium coupled transports and anion exchangers are involved in organic anion reabsorption.