More than 25% of the population suffer from Type I allergy, an IgE-mediated hypersensitivity disease. Allergens with homology to the major birch ( Betula verrucosa ) pollen allergen, Bet v 1, belong to the most potent elicitors of IgE-mediated allergies. T1, a cytokinin-inducible cytoplasmic periwinkle ( Catharanthus roseus ) protein, with significant sequence similarity to members of the Bet v 1 plant allergen family, was expressed in Escherichia coli. Recombinant T1 (rT1) did not react with IgE antibodies from allergic patients, and failed to induce basophil histamine release and immediate-type skin reactions in Bet v 1-allergic patients. Antibodies raised against purified rT1 could be used for in situ localization of natural T1 by immunogold electron microscopy, but did not cross-react with most of the Bet v 1-related allergens. CD analysis showed significant differences regarding secondary structure and thermal denaturation behaviour between rT1 and recombinant Bet v 1, suggesting that these structural differences are responsible for the different allergenicity of the proteins. T1 represents a non-allergenic member of the Bet v 1 family that may be used to study structural requirements of allergenicity and to engineer hypo-allergenic plants by replacing Bet v 1-related allergens for primary prevention of allergy.