This Core will breed congenic mouse strains required for three of the four projects of the Center. Five knockout (null) mice strains and corresponding congenic wild-type mice and one conventional transgenic and corresponding wild-type congenic littermate will be bred and provided to the Project Leaders of individual projects for experimentation. The utilization of congenic mouse strains will circumvent the potential problem of confounding effects contributed by differences at genetic loci other than those being tested. For two of the null transgenic strains, mutant and wild-type congenic derivatives will be generated using the "speed congenics" procedure which can generate congenic lines differing at less than 0.5 percent of the genome within five generations, rather than the ten required for the conventional congenic procedure. All congenics will be generated in the C57BL/6 mouse strain, which we have developed as a model for DEP-induced allergic hyperresponsiveness. Another service of the Core will be to genotype mice for the transgenic mutations. Two mouse strains, that are yet to be obtained from other collaborators, may be infected. If necessary, the Core will be responsible for rederiving these strains. In one project, mice will be exposed to TCDD, which is a potent carcinogen. The Core will be responsible for exposing the mice to TCDD in an acceptable and safe fashion, and for appropriate handling of contaminated material.