A composition comprising therapeutically effective amounts of two or more overlapping fragments of any part of preproinsulin (wherein one fragment is antigenic) and a pharmaceutically acceptable carrier for use in the treatment or prophylaxis of insulin dependent type I diabetes mellitus is disclosed wherein the composition may act by causing immunological tolerisation to insulin, preproinsulin or proinsulin and thus alleviate the effects of autoimmune disease in the pathogenesis of diabetes via the generation of anti-insulin antibodies. The composition may comprise fragments of overlapping sequence of 1-20 residues, may be formulated with alum or Freunds adjuvant and may be provided in a kit together with a diagnostic test for diabetes. The composition may further comprise other peptide fragments and may comprise two antigenic fragments from preproinsulin. Methods of treating type I diabetes are also disclosed.
