Rush immunotherapy with a standardized and lyophilized cocksfoot pollen extract was performed in twenty-three allergic subjects and compared with classical immunotherapy done with an alum adjuved, pyridine extracted cocksfoot pollen extract (fifteen subjects) and a control group of ten patients. The three groups were perfectly matched. Clinical benefits were analysed by means of symptom scores. It was shown that rush immunotherapy gave significantly better results when asthma or rhinitis was considered than either classical immunotherapy (P less than 0.02) or in the control group (P less than 0.01 and 0.02). Skin tests were significantly reduced after rush immunotherapy and did not change in the two other groups. After the pollen season the skin test reactivity was increased in the rush immunotherapy group. Cocksfoot pollen specific IgE did not vary significantly in the three groups. Cocksfoot pollen specific IgG was significantly (P less than 0.05) increased in the rush immunotherapy group before the pollen season and did not vary significantly in the other groups.