In a previous study, 39 adults with grass pollen allergy were hyposensitized for approximately 21/2 years. Treatment was performed in a double-blind fashion with extract made from timothy grass - either Alutard SQ, 20-component extract or a purified 2-component extract, including only the two major allergens Phi p V and VI. Standardized symptom + medicine scores and challenge tests demonstrated a clinical effect, most markedly in the group receiving 20-component extract. Six years after termination of treatment, 38 patients could be approached and 16 in each group were examined and repeated symptom scoring during the subsequent season. When adjustment for variations in pollen counts were made, medicine + symptom scores stayed low during the follow-up period. Specific IgE-antibodies against timothy showed an increase to initial values during the same period, whereas total IgE antibodies remained low. Skin prick test reactions with timothy allergen tended to increase but were still smaller than before treatment. Retrospectively, the patients reported symptoms to have stabilized or even further decreased after termination of treatment, with no significant difference between groups. In conclusion, the clinical effect was still present more than 6 years after termination of treatment. Some in vitro parameters tended to return to pretreatment level. The spontaneous course of the disease in non-hyposensitized patients was not investigated.