Comparison of Different Up-dosing Schedules With Osiris Phleum Pratense

Inclusion Criteria: * Written informed consent obtained before entering the trial * Male or female \>/= 18 years at visit 1 * A clinically relevant history of grass pollen induced allergic rhinoconjunctivitis (moderate to severe) and having received symptomatic treatment during grass pollen season 2010 and 2011 * Positive skin prick test response (wheal diameter \>/= 3mm) to Phleum pratense * Positive specific IgE against Phleum pratense (\>/= 0,70KUL / class 2) * Female subjects of childbearing potential must have a negative pregnancy test and be willing to practice appropriate contraceptive methods until Visit 4 * Subjects willing and able to comply with trial protocol regimen Exclusion Criteria: * Subjects included in another protocol (treatment intervention and/or investigational medicine product) or having participated in another clinical trial within 30 days prior to visit 1 * A clinically relevant history of symptomatic seasonal allergic rhinoconjunctivitis caused by an allergen (e.g. hazel, alder, birch, ash) to which the subject will be exposed during the 30-day treatment period. * A clinically relevant medical history of symptomatic perennial allergy to allergen(s) to which the subject is regularly exposed (e.g. cat, house dust mites). * Known sensitization (history of positive SPT) to food allergens with oral allergy syndrome * Uncontrolled asthma (in accordance with GINA guidelines) within the last 12 months * FEV \< 60% of predicted within the last 12 months * Severe asthma exacerbation(s) within the last 12 months * A clinically relevant chronic disease (\>/= 3 months) (e.g fibrosis, malignancy, type 1 diabetes mellitus, malabsorption or malnutrition, renal or hepatic insufficiency) * Malignancy or systemic disease affecting the immune system (e.g. autoimmune disease, immune complex disease or immune deficiency disease) * Inflammatory conditions in the oral cavity with severe symptoms such as oral lichen planus with ulcerations or severe oral mycosis or dental extraction at randomisation * Medical history of recurrent urticaria or atopic dermatitis during the last 2 years * Currently receiving treatment preventing the initiation of SIT (e.g. tricyclic antidepressants, mono amine oxidase inhibitors (MAOIs) and catechol-O-methyl transferase inhibitors (COMT inhibitors)) * History of allergy, hypersensitivity, or intolerance to the excipients of the investigational medicinal product * Being immediate family of the investigator or trial staff, defined as the investigator's / staff's spouse, parent, grandparent, child or grandchild * History of drug induced (incl. immunotherapy) facial angioedema (including experience of Quincke oedema) or a family (parents or siblings) history of hereditary angioedema * Anticipated use of any prohibited medication within the specified time windows as defined in the protocol * Previous treatment by immunotherapy with grass pollen for more than one month within the last 5 years * Any clinically significant condition or situation, other than the condition being studied, that in the opinion of the investigator would interfere with the trial evaluations or optimal participation * History of anaphylaxis with cardio respiratory symptoms (e.g. food allergy, drugs or an idiopathic reaction)