Inclusion Criteria:

• If the volunteer is female of childbearing potential, she must demonstrate a negative urine pregnancy test and agree to remain abstinent or use an effective method of birth control
• Positive skin prick test to ragweed pollen allergen extract
• Positive skin prick test to positive histamine control
• Negative skin prick test to negative control; redness, but no wheal is acceptable
• The subject must demonstrate a specific IgE for ragweed with class >= 2.
• The subject must have clinically acceptable results from the screening procedure including blood pressure (BP), heart rate (HR), electrocardiogram (ECG), physical examination, medical history, hematology, biochemistry, infection screen (hepatitis B antigen, hepatitis C antibody, HIV), urine pregnancy test, urinalysis, drugs of abuse screening panel and saliva alcohol testing

Exclusion Criteria:

• History or presence of acute or subacute atopic dermatitis, chronic dermatitis, urticaria factitia, or urticaria due to physical/chemical influence or any other skin conditions which might interfere with the interpretation of skin prick test results
• Visual inspection of the forearms indicates potential problems with the conduct or interpretation of the skin prick tests; both forearms must be available for testing
• Subject has asthma or other lower respiratory tract condition
• History or presence of diabetes, cancer or any clinically significant cardiac, metabolic, renal, hepatic, gastrointestinal, dermatologic, venereal, hematologic, neurologic or psychiatric diseases or disorders
• Any clinically significant abnormal laboratory value at Visit 1
• Clinically relevant sensitivity to any of the following common perennial or seasonal allergens: house dust mites, molds, epithelia, grass pollen mix, plantain, orache, nettle, mugwort, bermuda grass
• Clinically relevant symptoms due to an IgE–mediated allergy at screening and before inclusion to the treatment period
• Secondary alteration at the affected organ
• History of auto-immune diseases or rheumatoid diseases
• Medical condition that prohibits the use of adrenaline
• Disorder of tyrosine metabolism
• Diseases interfering with the immune response and having received medication which could influence the results of this study
• Subject has acute or chronic infection
• History of anaphylaxis
• Subjects determined by the Investigator to have any medical condition that could jeopardize their health or prejudice the results
• History of hypersensitivity to the excipients of the study medication
• History of immunotherapy with ragweed allergen extracts
• Current therapy with ß-blockers
• Currently receiving anti-allergy medication or other drugs with an antihistaminic activity
• Subject has a positive drugs of abuse screen at Visit 1
• Subject participated in a clinical trial and has taken investigational drug within the last 30 days
• Subject cannot communicate reliably with the Investigator or is deemed uncooperative or noncompliant
• Females who are pregnant, breastfeeding, or refuse to use a reliable method of birth control
• Subject received treatment with a preparation containing MPL during the past 12 months
• Use of prohibited medications or inadequate washout periods prior to screening