A clinical trial of pre-seasonal hyposensitization with intra-nasal grass pollen extract was carried out in forty-two patients. Results were assessed subjectively, by clinical examination during the pollen season, and by measurements of nasal air flow. Useful relief of symptoms was considered to have occurred in fifteen out of twenty-one patients who had pre-seasonal treatment with pollen extract and in five out of twenty-one patients who had similar treatment with carbol saline as a placebo. Of twelve patients who were symptom free in the pollen season ten had nasal hyposensitization. It is concluded that this simple and safe method of treatment gives results comparable with those of pre-seasonal injections.