The effect of treatment with astemizole (Hismanal) on symptoms elicited by ingestion of hazelnuts in birch pollen-allergic patients (the oral allergy syndrome) was investigated. Thirty patients with a well-documented allergy to silver birch, experiencing symptoms when ingesting hazelnuts, were included in the study. All had a positive skin prick test (SPT) to birch, whereas 29 and 27, respectively, showed a positive RAST and basophil histamine release test (HR) to birch. In contrast, only 15 patients had a positive SPT to hazelnut, 13 had a positive RAST, whereas 24 had a positive HR. After two oral provocations with hazelnuts the patients were randomized to receive either 10 mg of astemizole or placebo daily for 2 weeks in a double blind protocol followed by two oral provocations. Treatment with astemizole significantly reduced the symptoms compared with placebo (P = 0.004); however, without completely abolishing the symptoms.