An in vitro conifer ectomycorrhizal model system was developed to study changes in gene expression during the establishment of symbiotic relationship. Using the model system and the mRNA differential display technique, we have identified cDNA clones from Laccaria bicolor that appear to be involved in establishing and maintaining the symbiotic relationship between L. bicolor and red pine. These differentially expressed cDNA clones were obtained from mRNA extracted from the fungus 6–24 h after initiation of interaction. BLAST analysis showed that sequences of these clones did not match with any of the previously characterized genes. The cDNAs had regions with varying degrees of similarity to genes involved in signal transduction and transcriptional activation.