Abstract Ambrosia artemisiifolia(ragweed) is a neophyte in Europe and Germany, which originated from the United States of America. In the USA the rate of sen-sitization against ragweed equals that of grass pol-len, and without containment the rate of allergic sensitizations against ragweed pollen will clearly in-crease. Currently, the most frequent sensitizations in Germany are against grass pollen, followed by sensitizations against house dust mite and birch pollen. Ragweed pollen evokes symptoms at about
10 pollen/m 3, grass pollen at about 15 pollen/m 3. ese concentrations of ragweed pollen are only reached on limited occasions in Germany.