Spotted complementary DNA microarray analysis was performed on lungs of six selected strains, including the two parental strains and the unresponsive strain. This analysis revealed approximately 50 genes that were consistently induced at least twofold by lipopolysaccharide in the responsive strains. Some, but not all, of these genes have been previously associated with the biological response to lipopolysaccharide. Genes not previously linked to the lipopolysaccharide response might represent novel molecular targets for therapeutic intervention. Most of the genes up-regulated in the responsive strains were unchanged in the unresponsive strain; however, some genes in the latter were also significantly up-regulated, providing clues to the nature of the recessive mutation.