The BcA86 strain is a unique recombinant congenic strain created from parental strains A/J and C57BL/6J. Naive mice from the BcA86 strain have a lung responsiveness phenotype resembling mice from airway hyperresponsive strain A/J. However, majority of the BcA86 genome is from the hyporesponsive strain C57BL/6J. Our goal was to identify the genomic regions that are associated with this BcA86 phenotype. Using F2 mice generated from BcA86 backcrossed to C57BL/6J, we identified a QTL for airway hyperresponsiveness on mouse chromosome 12. We validated the importance of mouse chromosome 12 in airway responsiveness using a chromosome 12 substitution strain (CSS12) which contains A/J chromosome 12 on a C57BL/6J background. The CSS12 strain also had a lung responsiveness phenotype similar to A/J. We selected genes within our QTL as candidates for airway hyperresponsiveness if they contained a deleterious coding variant (based on PROVEAN analysis) or if they were differently expressed between hyperresponsive (A/J, BcA86, CSS12) and hyporesponsive (C57BL/6J) strains.