Oral immunotherapy (IT) was evaluated in a pilot study in two centres in children aged 8–15 years with allergic rhinoconjunctivitis. High doses (up to 20 × 106 BU monthly) of a defined freeze-dried birch pollen extract administered in enteric-coated gelatine capsules were given either daily for seven consecutive days every month or once weekly. Symptom scores, as assessed by sneezing, dripping and blockage of the nose, and redness, itching and swelling of the eyes, were significantly lower in treated patients compared to untreated, or placebo treated controls after 3 to 5 months of therapy. In all the 16 treated, but only in three of eight untreated patients, the scores were lower during the pollen season 1982 than during the pollen season preceding the treatment period, despite comparable pollen counts during the two seasons. One year after beginning treatment the reactivity in conjunctival provocation tests was decreased about 10-fold (P < 0.001) in the patients receiving more than 2 × 105 BU monthly compared to about two-fold in patients receiving lower doses, or placebo. Increased levels of IgE antibodies directed against birch pollen were recorded in the serum and saliva of most patients after 3–4 months of active IT. In contrast, IgG antibody responses were poor in most of the patients. Side effects, particularly from the gastrointestinal tract, appeared in all treated children. In one of t hem a systemic reaction occurred during IT. The study indicates that properly performed oral IT with a potent birch allergen extract in enteric-coated capsules may be effective.