This multi-center, randomized, observer-blinded, placebo-controlled study will evaluate the safety and tolerability of subcutaneous doses of RO4989991 in patients with allergic rhinitis who are otherwise healthy. The anticipated time on study treatment is 2 weeks.

Inclusion Criteria:

• Adult patients, 18-65 years of age, inclusively
• A history of allergic rhinitis diagnosed by a physician, but otherwise healthy
• A positive skin prick test to at least one standardized allergen at screening
• A body mass index (BMI) between 18 and 32 kg/m2, inclusively

Exclusion Criteria:

• History or presence of any respiratory disease or condition other than allergic rhinitis
• Use of prescription medication or herbal remedies within 14 days of dosing the study drug
• Use of over-the-counter (OTC) medications within 7 days of dosing the study drug
• Acute infection (including viral infections) 6 weeks (8 weeks for respiratory infections) preceding dosing or any ongoing chronic infection
• Positive test for human immunodeficiency virus (HIV) or hepatitis B or C