Non-pathogenic binucleateRhizoctonia species (BNR) belonging to the anastomosis group AG-G are commonly associatedwith members of the Rhizoctonia solani complex. They provide effective protection to youngbean seedlings against root rot caused by R. solani AG-4. Both fungi are morphologicallysimilar and it is difficult to differentiate between them without using laborious conventionaltechniques. RAPD assays were carried out on a large range of isolates of binucleateRhizoctonia species to identify markers common to all AG-G isolates. Two fragments of 1368 bpand 882 bp were isolated, cloned and used to probe Southern blots of DNA from: AG-G isolates; isolatesfrom other AGs of binucleate and multinucleate Rhizoctonia species; various heterogeneouspathogens known to infect bean plants; and co-inoculated bean plants with BNR AG-G and R.solani AG-4. The fragments hybridized only to DNA from AG-G isolates. Both fragments werenucleotide sequenced and two pairs of SCAR (sequence characterized amplified region) primers (BR1aF/R and BR1b F/R) were generated for use in PCR. Two fragments of anticipated size weregenerated following PCR of all isolates of AG-G and not from any range of other fungal speciesassociated with root and leaf diseases of beans. The SCAR primers were also used to detect AG-Gisolates in DNA extracted from bean and soil samples co-inoculated with binucleate and multinucleateRhizoctonia species. The assays were capable of detecting as little as 2·6 pg offungal DNA in extracts of soil samples. This system offers the potential to determine the presence ofAG-G isolates in infected soil and plant samples.