Allergen-specific immunotherapy (SIT), the administration of gradually increasing quantities of an allergen extract to an allergic patient, is a curative approach which directly treats the underlying allergic disease. GrassMATAMPL has been developed to provide pre-seasonal specific immunotherapy for patients with an allergy to grass pollen (hay fever). The purpose of this double-blind Phase IIb study is to assess the tolerability and immunogenicity of different doses of GrassMATAMPL in volunteers allergic to grasses and rye pollen.