The novel derivatives of pepstatin have the general formula (I) below in which X, Y and Z, are identical or different, and each represent an amino-acid selected from arginine, glutamic acid, aspartic acid, lysine, histidine and valine, the carboxyl function of the terminal amino-acid being esterifiable. The indices a, b and c are each equal to zero or 1, the sum a+b+c being equal to 1, 2 or 3. The invention also includes the water soluble salts and their preparation, and the compositions containing them. ##STR1## These novel products are particularly useful in the diagnosis and treatment of arterial hypertension due to the action of renine.