The invention relates to grass pollen extracts containing reduced amount of flavonoid glycosides in order to minimize the risks of genotoxicity of the grass pollen extracts. The invention also relates to a method of preparing grass pollen extracts containing reduced amount of flavonoid glycosides by ultrafiltration. Flavonoid glycosides are naturally present in grass pollen extracts and they have been identified as being responsible for the formation of flavonoid aglycones, which are genotoxic in vitro, under the influence of enzymes contained in the grass pollen extracts.
