Cre cDNA was inserted at the start ATG of the Tbx21 gene in a BAC (RP23-237M14). The recombined BAC was linearized and injected into B6/CBA oocytes. 14 animals were generated and one was determined to be positive for the Tbx21-cre transgene. The single founder line was analyzed by immunohistochemistry for cre protein. Strong expression was detected and reporter crosses displayed recombination in the mitral and external tufted layers of the main and accessory olfactory bulbs, with no other brain tissues showing recombination. Activity was also observed in the thymus, a known site of Tbx21 expression.