α-Casozepine and f91–97, peptides from α_s1-casein, display anxiolytic activity in rats and may have to cross the intestinal epithelium to exert this central effect. We evaluated their resistance to hydrolysis by the peptidases of Caco-2 cells and their ability to cross the cell monolayer. To mimic physiological conditions, two preparations of bile salts were used in noncytotoxic concentrations: porcine bile extract and an equimolar mixture of taurocholate, cholate, and deoxycholate. The presence and composition of bile salts appeared to modulate the peptidase activities of the Caco-2 cells involved (i) in the hydrolysis of α-casozepine, leading to much higher formation of fragments f91–99, f91–98, and f91–97, and (ii) in the hydrolysis of f91–97, leading to lower degradation of this peptide. Transport of α-casozepine across Caco-2 monolayer increased significantly, in the presence of bile extract, and of fragment f91–97, in the presence of bile salts.