Phylogentically, the organic anion transporters 1 (OAT1) and OAT3 are closely related whereas OAT2 is more distant. Experiments with HEK293 cells stably transfected with human OAT1, OAT2, or OAT3 were performed to compare selected transport properties. Common to OAT1, OAT2, and OAT3 is their ability to transport cGMP. OAT2 interacted with prostaglandins (PGs) and cGMP uptake was inhibited by PGE₂ and PGF_2α with IC₅₀ values of 40.8 µM and 12.7 µM, respectively. OAT1 (IC50 23.7 µM), OAT2 (IC50 9.5 µM), and OAT3 (IC50 1.6 µM) were potently inhibited by MK571, an established multidrug resistance protein (MRP) inhibitor. OAT2-mediated cGMP uptake was not inhibited by short-chain monocarboxylates and, as opposed to OAT1 and OAT3, not by dicarboxylates. Consequently, OAT2 showed no cGMP-glutarate exchange. OAT1 and OAT3 exhibited a pH and a chloride dependence with higher substrate uptake at acidic pH and lower substrate uptake in the absence of chloride, respectively. Such pH and chloride dependencies were not observed with OAT2. Depolarization of membrane potential by high potassium concentrations in the presence of the potassium ionophore valinomycin left cGMP uptake unaffected. In addition to cGMP, OAT2 transported urate and glutamate, but cGMP-glutamate exchange could not be demonstrated. These experiments suggest that OAT2-mediated cGMP uptake does not occur via exchange with monocarboxylates, dicarboxylates, and hydroxyl ions. The counter anion for electroneutral cGMP uptake remains to be identified.