This study will be performed to determine the long-term efficacy of 19.000 BU Oralgen grass pollen administered daily in patients with grass pollen related allergic rhinoconjunctivitis.

Patients between 18 and 60 years will be randomized to receive either Oralgen grass pollen or placebo administered sublingually once a day. Treatment will start at least 16 weeks prior to the anticipated start of the pollen season 2009 and will last until the end of the pollen season 2011. Study medication will be titrated during the first period of treatment until maintenance dose has been reached.

Inclusion Criteria:

• male or female
• grass pollen related rhinoconjunctivitis symptoms for at least the last 2 pollen seasons
• positive skin prick test RRTSS greater or equal to 12 during the 2008 season
• signed informed consent

Exclusion Criteria:

• positive skin prick test for other environmental allergens and suffering from serious allergic symptoms
• clinical history of significant symptomatic allergic rhinitis due to tree/weed pollen which potentially overlap the grass pollen season
• clinical history of symptomatic perennial allergic rhinitis caused by an allergen to which the patient is regularly exposed
• lacking of good health
• abnormal spirometry
• lower respiratory tract infection
• asthma requiring treatment other than beta-2 agonists
• oral steroids within 12 weeks before screening
• regular contraindications for use of immunotherapy