Allergic symptoms in sensitized individuals are caused by proteins named allergens. We report here the cloning and the production of the cyclophilin Bet v 7, one of the birch pollen allergens. Recombinant Bet v 7 was produced in bacteria and used to raise a rabbit anti-Bet v 7 antiserum. With this antiserum we detected cyclophilin A in several pollen species and we demonstrated immunological cross-reactivity among those plant cyclophilins A by immunoblot and ELISA inhibition experiments. However, we could not detect cyclophilins in extracts of animal or mould origin with our anti-Bet v 7 antiserum. By inhibition experiments with purified mould cyclophilins, we confirmed the absence of cross-reactivity between plant cyclophilins and non-plant cyclophilins. In addition, our results indicate that the level of immunological cross-reactivity correlates with the level of sequence identity among the cyclophilin A family. This allowed us to define the plant cyclophilin A sub-family as being immunologically distinct, which might have implications at the clinical level in the allergy practice.