This was a phase 2, randomized, double-blind, placebo-controlled, parallel groups study conducted in 3 centers in the US (NCT00689299). Study drug was sublingually dosed once daily as 0.15 mL of US standardized cat hair extract dosed either undiluted, as 1:10 dilution, or placebo. Target dose was obtained on Day 3 of dose titration escalating through 1:100 and 1:10 dilutions on Day 1 and Day 2 in the high dose group or placebo and 1:100 dilutions in the low dose group. Treatment duration was 20 weeks. Adult (>18 years) study subjects had positive history for cat allergy without asthma, positive skin test to cat allergen, absence of immunotherapy during the prior 2 years, and absence of other confounding baseline conditions. The primary outcome parameter was average Total Symptom Score (TSS) during a 1-hour cat chamber exposure. TSS is the sum of 7 items rated from 0 - 3 (none to severe) for nasal symptoms (rhinorrhea, nasal congestion, nasal itching, and sneezing) and non-nasal symptoms (eye watering, eye itching, and itching palate/ ear/ throat).