This was a single centre, randomized, double-blind, placebo-controlled, parallel group study. The main aim of this study was to assess the effects of grass pollen immunotherapy on symptoms, bronchial hyperresponsiveness, and quality of life in seasonal rhinitis and asthma. Forty-four patients with severe summer hay fever (of whom 36 reported seasonal chest symptoms and 28 had seasonal bronchial hyperresponsiveness) participated in a randomised double-blind, placebo-controlled, parallel group study. After symptom monitoring for one summer, participants matched placebo injections (n=22) in a rapid up-dosing cluster regimen for 4 weeks, followed by monthly injections for 2 years. Outcome measures included hay fever symptoms and medication use, health-related quality of life, and measurements of non-specific bronchial responsiveness.