Various primary cells and an established cell line were cultured in roller tubes and in suspension to evaluate their potential roles as host cells to support the growth of M. leprae in vitro. The primary cells originated from the organs of chipmunks, mice and humans. Phagocytic ability of those cells except for macrophages was found to be low and did not vary much according to their origin. However, when macrophages from mice peritonial exudate were exposed to the bacteria, the phagocytic efficiency was higher than 47%. In spite of those good primary results, the macrophages are not cells which can adapt well in vitro for long term culture, which is essential for the growth of such a slow growing M. leprae. Thus, somatic cell hybridization between the macrophages and HeLa was made by fusing them with polyethylene glycole. Those hybrids appeared to have both the characteristics of the parent cells, which can provide a natural intracellular environment such as the macrophages and the infinite growth capability of the HeLa cells in vitro.