Recently we identified birch profilin as a novel pollen allergen which showed significant sequence homology with profilins from different eukaryotic organisms. Profilins were described to control actin polymerization and to participate in signal transduction via the phosphoinosite pathway, but have so far been unknown in plants. The ubiquitous occurrence of profilins in eukaryotes led us to the hypothesis that profilins may fulfill similar funtions in plants as known in other eukaryotes. Here we report on the identification of profilins as functional plant pan-allergens in distantly related plants. The ubiquitous occurrence of profilins in distantly related plants as allergenic structures provides a molecular basis for the frequently observed phenomenon of cross-sensitization towards distantly related plant species in allergic patients.