This was a single centre, randomised, double-blind placebo controlled trial of grass pollen injection immunotherapy (Alutard SQ, ALK Abello, Denmark) in adults with severe summer hayfever unresponsive to antihistamines and topical steroids. The main aim was to determine at which point in the dosing regime grass pollen immunotherapy causes a significant reduction in the late skin response to allergen challenge. A once weekly cluster regimen of 2 injections per visit was employed during the up-dosing phase, followed by monthly maintenance injections of 100,000 SQ units. Twelve patients received active treatment (mean age 31, 7 male) whilst 6 were given placebo (mean age 37, 2 male). The 24 hour skin response (size of swelling, (mm)) to intradermal allergen challenge (0.1, 1, 10 BU) was determined on alternate weeks during the 8 week up-dosing phase and then monthly up to 6 months and 3 monthly up to 11-13 months following initiation of treatment.