<b><i>Objective:</i></b> Many cellular responses to hypoxia are mediated by the transcription factor complex hypoxia-inducible factor (HIF). HIF stability is governed by a family of dioxygenases called HIF prolyl hydroxylases (PHDs). Isoquinolone-derived PHD inhibitors, like 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido) acetate (ICA), which stabilize the intracellular HIF-α have been suggested as a potentially beneficial therapeutic strategy for the treatment of disorders associated with ischemia. To stabilize HIF-α, ICA has to be taken up into proximal tubule cells (PCTs) across the basolateral membrane by one of the organic anion transporters 1, 2 or 3 (OAT1, OAT2 or OAT3). The release into the urine across the luminal membrane may be mediated by OAT4. <b><i>Method:</i></b> To demonstrate interaction of ICA with human OAT1, OAT2, OAT3 and OAT4, ICA was tested on these transporters stably transfected in HEK293 cells by using p-aminohippurate (PAH), cGMP and estrone-3-sulfate (ES) as reference substrates, respectively. <b><i>Results:</i></b> Uptakes of PAH and ES in OAT1- and OAT3-transfected HEK293 cells were inhibited by ICA with half-maximal inhibition values of 0.29 ± 0.05 and 2.58 ± 0.16 µ<smlcap>M</smlcap>, respectively. OAT2 was less sensitive to ICA. Efflux experiments identified ICA as an OAT1 and OAT3 substrate. Preloading OAT4-transfected HEK293 cells with ICA stimulated ES uptake by 18.3 ± 3.8%. <b><i>Conclusion:</i></b> The uptake of ICA across the basolateral membrane of PCTs occurs mainly by OAT1 and the efflux into the tubular lumen by OAT4.