The random amplified polymorphic DNA (RAPD) technique was used to develop DNA probes for the identification of ectomycorrhizal fungi belonging to the genus Tuber. RAPD fingerprinting revealed a high degree of interspecific variability and a low degree of intraspecific variability. One band (approximately 1.5 kb), consistently appearing when genomic DNA was amplified with an aspecific primer (OPA-18), was found to be a good marker for Tuber magnatum, and was used as a probe in Southern hybridization experiments. The specificity of the results suggests that this probe may be useful in developing specific primers for PCR amplifications.