Fifty-four adult patients with tree pollen-induced rhinitis (28), asthma (1), or rhinitis and asthma (25) were selected for immunotherapy with standardized and partly purified tree pollen extracts using a double blind protocol. The selection was based on clinical history, results of nasal or bronchial challenge, skin prick tests and RAST. Further, based on crossed radio-immunoelectrophoresis, sex, age and severity of symptoms, the patients were allocated in matched pairs and the treatment alternatives were randomly distributed within the pairs. Twenty-three patients treated with extracts composed of any combination of alder, birch and hazel pollen which matched their IgE response in CRIE (Group 1 (ABC)) and 22 patients receiving birch pollen extracts (Group 2 (B)) completed ail 3 years of treatment. The in vivo results comprising symptom and medicine consumption scores are given here. Changes in specific skin and nasal reactivity as well as in immunological parameters arc presented separately. No significant differences were demonstrated between the treatment groups in the two parameters. Both extracts were effective and reduced in general the symptom scores to one tenth of the starting level. Expressed another way, at the end of the study, the patients tolerated 30 times more pollen until symptoms of the same severity were elicited, compared to before. In the Nordic countries, spring-time asthma and rhino-conjunctivitis caused by pollen from deciduous trees can be effectively treated with an extract of birch pollen alone.