We have noted several patients suffering for rhinitis and/or asthma symptoms in the summer months without positive skin tests for pollens blossoming in the corresponding season. So we tried to determine the pollination pattern of pollens usually not tested, because no company produces the corrisponding extract.We determined airborne pollination by means of a volumetric pollen trap for five years from 2001 to 2005.We found, in addition to well-known aeroallergens, a significant percentage of Cannabaceae from the end of July to mid September with the highest concentration in 2004 (140 gr/m3).The potential allergenicity of Cannabis pollen was supported in the United States, where they found some patients with rhinitis or asthma during the pollen seasons and positive prick test for Cannabis, but the clinical significance of Cannabaceae pollen as an aeroallergen in Europe is still undefined.