Birch pollen and mugwort pollen allergies are often associated with hypersensitivity to plant foods. This clinical and serological cross-reactivity is mediated by IgE antibodies reacting with homologous proteins in pollen and food. Cross-reacting homologs of the important birch pollen allergen Bet v 2 (profilin) could be detected in other pollen, fruits, nuts, and vegetables, such as celery tuber. We purified IgG/IgE antibodies from the serum of an exclusively profilin-allergic patient using affinity columns either coupled with protein extracts from mugwort pollen, birch pollen, or celery tuber. Constrained and unconstrained random nonapeptide libraries were pooled and screened with the anti-profilin antibody preparations to define cross-reactive ligands. Specific ligands were enriched by successive panning rounds using the profilin-specific antibodies in series. After the last panning round enriched phage clones were screened with purified profilin-specific antibodies and IgE-binding clones were sequenced. Five out of eight positive clones (62.5 %) displayed the same circular peptide CAISGGYPVC. This peptide was synthesized and examined for its ability to inhibit IgE binding to blotted mugwort pollen, birch pollen, or celery tuber profilin. Inhibition studies showed reduction of IgE binding to profilins in all three protein extracts. As the sequence of the mimotope did not show any homology to the known birch profilin sequence this peptide is considered to mimic a common conformational IgE epitope for these examined profilins.