[en] The experiments have been performed in various conditions using ¹⁴C-PAH as a tracer. The relative ratio of the inhibitor constant (Ki) between Diodrast and probenecid was of the same magnitude as the concentrations of these inhibitors for maximal stimulation of PAH efflux. The author observed that in metabolically inhibited slices there was no PAH uptake against concentration gradient, but the efflux of PAH was greater than that in the normal slice. In these metabolically inhibited slice PAH efflux was also biphasically altered by Diodrast and probenecid added to the medium. When the concentration of sodium was reduced in medium, PAH influx was decreased but PAH efflux facilitated. 0.1mM disulfonic stilbene derivative, SITS (4-acetamido-4'-isothiocyano-2.2' disulfonic stilbene) increased PAH efflux in the normal slice, but decreased the efflux in the metabolically inhibited slice. Analyzing the data presented, the contractor came to the conclusion that the influx and efflux of PAH in the renal slice are mediated by mobile carrier cycling across the peritubular membrane of renal tubular cell. He observed also that the affinity of carrier for organic acids is altered by the energy-linking reaction at the cytoplasmic border of the membrane