Mugwort and ragweed pollens have been considered as important respiratory allergens in Korea. These two pollens are abundant in the air of Seoul from August through October. Many ragweed-sensitive patients have shown concurrent sensitivities to mugwort pollen. However the antigenic relationship between these two pollens has not been clarified. To observe the cross-reactivity between them, we developed polyclonal anti-mugwort and anti-ragweed antibodies by immunization on New Zealand white rabbits, and performed crossed immunoelectrophoresis(CIE) with two pollen extracts. Five precipitation lines were formed by mugwort and anti-mugwort antibody. One precipitation line was formed by ragweed and anti-ragweed antibody. There was no reaction from mugwort and anti-ragweed antibody, and from ragweed and anti-mugwort antibody. These results indicate that there is no cross-antigenicity between mugwort and ragweed pollens.