Leatherleaf fern has been imported from the United States, Honduras and Puerto Rico to the Federal Republic of Germany since 1966 and cultivated in Germany since 1970/71. It is slowly displacing the floral arrangements with asparagus used until now as filler and background material. This change is due primarily to its better keeping quality. Continuous contact with the leatherleaf fern induced an allergic contact dermatitis of the palms and fingers in a female florist. Patch tests with the leaf revealed the allergic origin of the dermatitis. Five fractions of a chromatographically separated extract of the fern were tested on sensitized guinea-pigs and on the patient. Only the first fraction gave a positive patch test response. By further separation colourless crystals of the contact allergen could be obtained. Elucidation of the structure is in progress. The sensitizer could only be detected during sporogenesis of the fern, that means when sporecapsules are present on the surface of the leaves.