Results: Significant reductions were observed in immunotherapy group compared with the placebo group in hay fever symptoms (49%, 15%: P = 0.1), medication scores (80%, 18%; P=.007), and seasonal chest symptoms (90%, 11%; P < .05). Impairment of overall quality of life (mean score of 7 domains) during the pollen season was less in the immunotherapy group than in the placebo group (median difference [95% CI], 0.8 [0.18-1.5]; P=.05=2]. During the pollen season, there was no change in airway methacholine PC20 (provocation concentration producing a 20% fall in FEV1) in the immunotherapy-treated group (P=5), compared with an almost 3 doubling-dose decrease in the placebo-treated group (P=.5), compared with an almost 3 doubling dose decrease in the placebo-treated group (P=.01, between-group difference). There were no significant local or systemic side effects during the study.