The Bordeles School of Le Coulant described in 1966, a contact dermatitis produced by "hepatics" of the Frullania genus. The hepatics together with the mosses and sphagnus form the group of Bryophytes. Only the hepatics with leaves or Jungermaniales have a capacity to cause sensitivity. They grow in dark colour plates on the bark of different trees such as the chestnut-tree, acacias, poplar-trees, beech-trees,and in particular, the oak-trees and evergreen oak-trees. The conifers are rarely affected by these epiphytes. The Frullania lives in the most adverse climates, growing not only on trees, but also on surfaces such as rocks, prefering humid sites. Cases of allergy to Frullania dilatata have been registered in France by Foussereau and Maleville and by De Graciansky. In British Columbia, Mitchel has described cases of contact dermatitis by another species of Frullania, the F. tamarisci subsp. nisquallensis. There are described six cases of contact dermatitis induced by Frullania dilatata that have been studied in the last five years. The indicated growth, because it is epiphyte on forest species, sensitizes those people who through their profession or way of life, come into contact with trees or wood. All our cases were men who had some sort of contact with oak-trees. The lesions fundamentely affected the face, hands and genitales; the diagnostic was established through a patch test with the plant itself. The lesions were of acute eczema so much macroscopic as well as mircoscopic. It has been proved that the responsible substance of the sensitization belongs to the group of sesquiterpenics lactons and that it is also responsible for the contact dermatitis produced by the chrysanthemum, ragweed, pyrstrum, etc. In one of the cases reported, a positive contact test was obtained using extract of chrysanthemum, and in the other case a hyposensitization was tried but it gave negative results.