Mast cells (MCs) play crucial roles in innate immunity to parasitic and bacterial infections as well as in hypersensitivity, such as the induction and exacerbation of allergy and autoimmune diseases. The regulatory mechanisms for MC development and effector functions are of great interest for developing novel therapeutic strategies against such disorders. Here we report the establishment of novel, immortalized MC lines from bone marrow (BM) cells of a temperature-sensitive mutant of SV40 large T antigen-transgenic mice (termed SVMCs). BM cells from tsSV40LT mice were cultured in the presence of interleukin (IL)-3 for 3 weeks, and then subjected to limiting dilution and single-cell cloning, yielding 27 independent MC clones, three of which were subjected to further analysis. On culture with nerve growth factor, stem cell factor and IL-3, these SVMC clones showed morphologic and biochemical changes from mucosal MC-like to connective-tissue MC-like phenotypes. These SVMC lines exhibited a significantly enhanced proliferation rate, and a higher responsiveness to the high affinity Fc receptor for IgE-mediated intracellular calcium mobilization and degranulation than those of BM-derived cultured MCs. These cell lines should facilitate studies on the mechanisms for the development, differentiation and effector functions of MCs in health and diseases.