Characterization of plant resistance genes is an important step in understanding plant defense mechanisms. Fusarium oxysporum f sp lycopersici is the causal agent of a vascular wilt disease in tomato. Genes conferring resistance to plant vascular diseases have yet to be described molecularly. Members of a new multigene family, complex l2C, were isolated by map-based cloning from the 12 F. o. lycopersici race 2 resistance locus. The genes show structural similarity to the group of recently isolated resistance genes that contain a nucleotide binding motif and leucine-rich repeats. Importantly, the presence of l2C antisense transgenes abrogated race 2 but not race 1 resistance in otherwise normal plants. Expression of the complete sense l2C-1 transgene conferred significant but partial resistance to F. o. lycopersici race 2. All members of the l2C gene family have been mapped genetically and are dispersed on three different chromosomes. Some of the l2C members cosegregate with other tomato resistance loci. Comparison within the leucine-rich repeat region of l2C gene family members shows that they differ from each other mainly by insertions or deletions.