Twenty patients with a proven sensitization to grass pollens were treated with parenteral “priming” and subsequently with either oral “booster” (n-10) or placebo (n=10) extension course. The study was carried out in a double-blind manner. Cumulative preseasonal parenteral dosage was 3,100 NU (Noon Units), patients in the oral group subsequently received 123.9 mg of grass pollen extract during the pollen season. No side effects were noted after intake of the oral preparation. No significant differences (95% confidence interval) were noted comparing results of in vivo (skin prick test and conjunctival provocation test) and in vivo tests (specific serum IgE- And IgG-antibodies) between the two groups. Analysis of symptom and medication scores as well as subjective assessment of patients revealed no superiority of oral “booster” over placebo. Data obtained in this study does not support the concept of combined parenteral and oral treatment. This is in contrast to work reported previously.