Pollen germination of invasive species<em> Impatiens parviflora</em> DC. is investigated in different mediums separately and together with pollen grains of other plants using method in vitro. The score which characterize direction and intensity of different plants pollen interference – IAS (antagonism–synergism index) – is devised. The inhibition of pollen grains germination of Impatiens parviflora by pollen <em>Rudbeckia</em> <em>hirta </em>L., <em>Rubus serpens</em> Weihe ex Lej. &amp; Court. and stimulation by pollen <em>Lysimachia nummularia</em> L. is observed. The methodology of two-factor experiment is revealed that the presence of antagonist species (biological agent) more severely increased effectiveness of pollen germination Impatiens parviflora than the presence of physiologically active substances (chemical agents).