B-cell translocation gene 2 (BTG2) belongs to the anti-proliferative gene family. According to previous in vitro studies, BTG2 overexpression leads to delayed cell cycling. We investigated BTG2 expression during mouse ontogeny and its immune and circadian functions in this study. In situ hybridization showed that BTG2 was expressed at high levels in the central nervous system, liver, stomach, thymus, spleen, skin, adrenal gland, pituitary gland and salivary glands during embryonic days (E10-E17), postnatal days (P1 and P10) and adult stages. Expression was observed in organs and tissues from adult mice with and without a robust proliferation program. Thus, the gene might have important functions that are both related and unrelated to proliferation. BTG2 expression was induced after in vitro T-cell receptor stimulation in T cells using anti-CD3 antibodies. However, transgenic (Tg) mice with actin promoter-driven expression of BTG2 showed normal in vitro and in vivo T-cell responses, such as thymus development, T-cell activation marker expression, T-cell proliferation and migration, as well as in vivo delayed-type hypersensitivity reactions. Although BTG2 was expressed in the suprachiasmatic nucleus and pineal gland in the brain, BTG2 Tg mice had no abnormal circadian behavior. Our data on BTG2 expression during ontogeny provide useful clues for the further investigation of BTG2 function. Additional studies are warranted to examine its role in immune and other systems.