Citrinin, a secondary product of fungal metabolism, is nephrotoxic in the rat. Because citrinin is an organic anion, it might be expected to be transported by the renal organic anion transport system. Rat renal cortical slices were used to characterize the transport. 14C-Citrinin uptake was enhanced by lactate and reduced by probenecid, a specific inhibitor of anion transport. Dinitrophenol is a metabolic inhibitor as well as competitive inhibitor of anion transport, and it also reduced citrinin transport. Organic cations did not alter citrinin accumulation by the slices. These data are consistent with the transport of citrinin by the renal organic anion secretory system.