Our objective is to know the incidence and characteristics of the sensitization to the pollen of Parietaria in the area of Bilbao. In a sample of 380 patients unselected, they have been achieved skin tests with Parietaria J. It has been found a sensitivity incidence of 4.2% of the total sample, and an incidence of 12% in relation to the number of patients with pollinois. A good correlation has been observed between the results of the skin tests and the RAST. The high levels of pollilisation (100 g/m3, on the 12th of August) and the incidence of the sensitization, show that the pollen of Parietaria is an important allergen in our area.