To establish an efficient screening system for differentially expressed genes of a phytopathogenic fungusColletotrichum lagenarium,we constructed an equalized (normalized) cDNA library fromC.lagenariumand used this library for differential screening. For the isolation of genes involved in infection-related developments of conidia, conidia undergoing appressorium differentiation were selected as the source of materials for construction of the cDNA library. The equalization of cDNA was performed twice using a kinetic method, and the products were cloned into a plasmid vector. Colony hybridization with nine probes of different abundance showed a reduction in abundance variation from at least 276-fold in the original library to 10-fold in the equalized cDNA library, which demonstrated that the cDNA was successfully equalized. By differential hybridization of 1900 cDNA clones in the equalized cDNA library and RNA blot analysis of candidate clones, we identified 11 independent cDNA clones, designatedCAD1throughCAD11, that were expressed in appressorium-differentiating conidia, but not in vegetative mycelia. The transcripts ofCAD1andCAD2hardly accumulated in preincubated conidia, whereas those ofCAD3andCAD4accumulated highly and slightly, respectively. The amount of the fourCADtranscripts increased at the early stage of the appressorium formation process. Sequence analysis ofCAD1revealed thatCAD1would encode for 101 amino acid polypeptides, which showed homology to metallothioneins. Deduced amino acid sequence ofCAD2would encode 278 amino acid polypeptides, and showed high homology to genes in aflatoxin, and sterigmatocystin gene clusters ofAspergillus parasiticusandA. nidulans, respectively.Key words: equalized cDNA library, differential screening,Colletotrichum lagenarium, appressorium formation,CADgenes.