Derivatives of glucagon-like peptide I (GLP-1) and especially GLP-1 (7-37) have been found to have insulinotropic activity. The invention pertains to a composition comprising an acid addition salt of GLP-I (7-37) and to a composition comprising a carboxylate salt of GLP-I (7-37). The invention also pertains to method of treating type II diabetes mellitus by providing derivatives of GLP-I (7-37) to the patient.