Dander from the domestic cat (Felis domesticus) is one of the most common causes of IgE mediated allergy. The present invention relates to a recombinant folded Fel d 1 with molecular and biological properties similar to the natural counterpart and specifically a synthetic gene coding for a direct fusion of Fel d 1 chain 2 N-terminally to chain 1. E coli expression resulted in a non-covalently associated homodimer with an apparent molecular weight of 30 kDa defined by size exclusion chromatography, each 19177 Da subunit displayed a disulfide pattern identical to that found in the natural Fel d 1, and having identical fold of natural and recombinant Fel d 1. The, recombinant Fel d 1 provides for diagnosis and allergen specific immunotherapy of cat allergy.