The purpose of this study is 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. Symptom scores and need of rescue medication were recorded by patients during the study period. The size of early and late cutaneous response to allergen challenge was recorded and measured by a physician.