These transgenic mice express Cre recombinase from the mouse Tbx21 (T-box 21; also called Tbet) promoter in mitral cells of the main and accessory olfactory bulbs. Surveys of the rest of the brain show that Cre-induced recombination is specific to the olfactory bulbs and occurs by E14.5 in the developing mitral cell layer. Cre-mediated recombination has also been demonstrated in the thymus. Homozygotes are viable and fertile, and are phenotypically normal. Mitral and tufted cells demonstrate lacZ staining in progeny derived from crosses with a floxed STOP lacZ reporter strain (e.g. Stock No. 003474). Crosses with a floxed Stop hChR2(H134R)-tdTomato fluorescent reporter strain (see Stock No. 012567) enable direct optogenetic activation of mitral and tufted cells in the olfactory bulb.