Winter wheat (Triticum aestivum) shows local, induced resistance against the plant-pathogenic fungus Erysiphe graminis f. sp. tritici following exposure to the nonpathogen E. g. f. sp. hordei. The onset of this resistance has been shown to be correlated with the activation of putative defense genes, and cDNA clones representing transcripts of induced genes have been obtained (P. Schweizer, W. Hunziker, and E. Mösinger, Plant Molecular Biology 12:643-654, 1989). We have cloned and sequenced a gene corresponding to one of these cDNAs, WIR5. Sequence analysis indicated that this gene contains three exons and encodes a protein of 229 amino acids. S1 mapping showed that transcripts homologous to this gene are at least 20 times more abundant in leaves infected 14 hr earlier with E. g. f. sp. hordei than in control leaves. Sequence comparison showed that the WIR5 gene product is highly homologous to glutathione-S-transferases (GSTs; EC 25.1.18) of maize. This, together with the fact that the intron positions of both the wheat gene and the maize GSTI gene are conserved, suggests that the cloned pathogen-induced gene, named GstA1, encodes a wheat glutathione-S-transferase.