Using a subtractive hybridization (SH)/cDNA-AFLP combinational approach,differentially expressed genes involved in the potato-Phytophthora infestans interaction were identified.These included genes potentially controlling pathogenesis or avr genes in P.infestans as well as those potentially involved in potato resistance or susceptibility to this pathogen.Forty-one differentially expressed transcriptderived fragments (TDFs),resulting from the interaction,were cloned and sequenced.Two TDFs,suggested as potential pathogenicity factors,have sequence similarity to N-succinyl diaminopimelate aminotransferase and a transcriptional regulator,TetR family gene,respectively.Two other TDFs,suggested as potential avr genes,have sequence similarity to an EST sequence from Avr4/Cf-4/Avr9/Cf9 and a P.infestans avirulence-associated gene,respectively.Genes’ expression and origin were confirmed using Southern blots,Northern blots and qRT-PCR.I.e.,potential resistance gene DL81 was induced at 12 hpi in the moderately resistant cultivar,whereas it was down-regulated as early as 6 hpi in the susceptible cultivar.On the other hand,DL21 was induced at 6 hpi (3.38-fold) in response to the highly aggressive isolate (US8) and strongly up-regulated thereafter (25.13-fold at 120 hpi.),whereas it was only slightly up-regulated in response to the weakly aggressive isolate US11 (3.82-fold at 96 hpi),suggesting its potential involvement as a susceptibility gene. Using a subtractive hybridization (SH) / cDNA-AFLP combinational approach, differentially expressed genes involved in the potato-Phytophthora infestans interaction were identified. These found genes potentially contributing to pathogenesis or avr genes in P. infestans as well as those potentially involved in potato resistance or susceptibility to this pathogen. Forty-one differentially expressed transcript derived fragments (TDFs), resulting from the interaction, were cloned and sequenced. Two TDFs, suggested as potential pathogenicity factors, have sequence similarity to N-succinyl diaminopimelate aminotransferase and a transcriptional regulator, TetR family genes, respectively. Two other TDFs, suggested as potential avr genes, have sequence similarity to an EST sequence from Avr4 / Cf-4 / Avr9 / Cf9 and a P.infestans avirulence-associated genes, respectively. Genes expression and origin were confirmed using Southern blots, Northern blots and qRT-PCR.Ie, potential resistance gene DL81 was induced at 12 hpi in the moderately resistant cultivar, yet it was down-regulated as early as 6 hpi in the susceptible cultivar. On the other hand, DL21 was induced at 6 hpi (3.38-fold) in response to the highly aggressive isolate (US8) and strongly up -regulated thereafter (25.13-fold at 120 hpi.), but it was only slightly up-regulated in response to the weakly committed isolate US11 (3.82-fold at 96 hpi), suggesting its potential involvement as a susceptibility gene.