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Objectives This study was designed to investigate the effects of Sho-saiko-to (Xiao Chai Hu Tang), a Chinese traditional medicine, on the membrane permeability of tolbutamide in the intestinal tract. We carried out an in-situ loop study with rat jejunum and a transport study with Caco-2 cell monolayers. Methods In the in-situ loop study, absorption clearance of tolbutamide was estimated from the drug concentrations in the loop and plasma. The apical-to-basolateral and basolateral-to-apical transport of tolbutamide and d-mannitol, a paracellular transport marker, was assessed using Caco-2 cell monolayers cultured on a polycarbonate membrane. Key findings The absorption clearance of tolbutamide was enhanced by a concomitant dose of Sho-saiko-to over 10 min in the rat in-situ loop. Sho-saiko-to increased the apical-to-basolateral transport of tolbutamide, whereas the basolateral-to-apical transport of this drug was reduced by Sho-saiko-to. On the other hand, in both directions the Papp of d-mannitol was reduced by the presence of Sho-saiko-to. Furthermore, the apical-to-basolateral transport of tolbutamide in ATP-depleted Caco-2 cells was diminished by Sho-saiko-to. These findings suggest that Sho-saiko-to can facilitate the epithelial membrane permeability of tolbutamide across the rat jejunum in-situ and Caco-2 cell monolayers. Since Sho-saiko-to suppressed the passive transport of tolbutamide from the apical-to-basolateral side, enhanced permeability may be related to effects of Sho-saiko-to on the energy-dependent transport of tolbutamide in the intestine. Conclusions Our findings suggest that Sho-saiko-to might facilitate the energy-dependent transport of tolbutamide across the rat jejunum in-situ and Caco-2 cell monolayers.