Enzyme-linked immunosorbent assay with rabbit polyclonal antibodies developed to isolated exopolysaccharide of Paenibacillus polymyxa 1465 was used to evaluate the colonization of wheat-seedling roots by this bacterium. The assay conditions were optimized for detection of the P. polymyxa exopolysaccharide determinants forming part of the samples used (homogenates of inoculated roots). The dynamics of the immunoenzymatic revealing of specific polysaccharidic antigenic determinants in the samples' composition correlated with an increase in P. polymyxa numbers on the roots found by estimation of colony-forming units.