Antigenic properties and serological relationship was investigated in binucleate and multinucleate Rhizoctonia spp. isolates from strawberries soybean, alfalfa and potato plants from Serbia, from Spain, anastomosis group testers and in strawberry roots inoculated with binucleate Rhizoctonia AG A and AG I. Two polyclonal antisera, unabsorbed and cross absorbed, were used in dot-immunobinding assay for these investigations. Antisera were produced against mycelial antigens of two isolates, which belong to different anastomosis groups (AG) of binucleate Rhizoctonia - AG A and AG I. Both unabsorbed antisera reacted positively with all tested Rhizoctonia spp. isolates, and the reaction was absent with control isolates (Pythium sp. Agaricus sp. and Fusarium sp). The results prove a close serological relationship among Rhizoctonia spp. isolates, and diversity between Rhizoctonia spp. and isolates from different taxonomic groups. Also, both unabsorbed antisera reacted with higher intensity with closely related antigens (belonging to the same AG) than with ones from another AG of binucleate Rhizoctonia or R. solani (multinucleate Rhizoctonia). After cross absorption specificity of the antisera was enhanced, especially with the antiserum raised against mycelial proteins of binucleate Rhizoctonia AG I. This antiserum reacted positively only with antigens from the same AG, after cross absorption with antigens from AG A of binucleate Rhizoctonia and from R. solani AG 2-2. It proved to be specific to AG I of binucleate Rhizoctonia, and able to differentiate isolates of this AG from others. In this way the serological homology among isolates of one AG was proven, and also the diversity among isolates which belong to different AGs of binucleate Rhizoctonia as well as isolates of R. solani.