Pharmaceutical composition

Phenylalinine derivatives having the general formula: and their non-toxic salts, have been found to promote the absorption of medicinal substances such as insulin. In the above formula, R' is a hydrogen atom, a fluorine atom, a nitro group, a hydroxyl group or a hydroxyl group protected by an esterifying group, X is -CO- or -SO2-, -Y- is a straight bond, a lower alkylene group, a substituted or unsubstituted vinylene group, or a group having the form- fula -CH2-O- or -0-CH2-, and R2 is a substituted or unsubstituted phenyl or naphthyl group; or the group R2-Y-CO- is an N-benzyloxy-carbonylphenylalanyl group, an N-benzyloxycarbonyl-4-flurophenylalanyl group or an N-(m-methoxycinnamoyl)phenylalanyl group.