Five taxon-specific oligonucleotide probes are described that can be used to help identify the fungal components of ectomycorrhizae. Comparisons among partial sequence from the mitochondrial large subunit rRNA gene (mt-LrRNA) were used to select the probes, which were intended to be specific to several taxa within the suilloid group of the Boletales (Basidiomycota). Probes S1, R1, and G1 were targeted at the genera Suillus, Rhizopogon and Gomphidius; probe G2 was designed to recognize the family, Gomphidiaceae, and probe US1 was designed to recognize all of these taxa and any other members of the suilloid group. The specificity of each probe was determined empirically by testing their ability to hybridize to PCR amplified fragments derived from 84 species of basidiomycetes. Although none of the probes exhibited their intended specificity, all specifically hybridized to useful subsets of taxa, and collectively they can be used to identify many suilloid taxa to the generic level or below. The probes were also tested for their ability to identify field collected mycorrhizae and were found to perform well.