The cloning of major resistance genes has led to a better understanding of the molecular biology of the steps for induction of resistance, yet much remains to be discovered about the downstream genes that collectively confer resistance, i.e. the defence response (DR) genes. We are dissecting the pathways contributing to resistance in rice by identifying a collection of mutants with deletions or other structural rearrangements in DR genes. The collection of rice mutants has been screened for many characters, including increased susceptibility or resistance to Magnaporthe grisea and Xanthomonas oryzae pv. oryzae. A collection of enhanced sequence tags (ESTs) and putative DR genes has been established to facilitate detection of mutants with deletions in DR genes. Arrays of DR genes will be used to create gene expression profiles of interesting mutants. Successful application of the mutant screen will have broad utility in identifying candidate genes involved in disease response and other metabolic pathways.