A peculiar adherent cell clone (R613BM) was established under muscle tissue free conditions from bone marrow of a Wistar rat. The cloned cell line was able to form myofibrils and expressed nicotinic acetylcholine receptors specific for skeletal muscles. The muscle specific characteristics have been maintained consistently for more than five years. These results suggest that bone marrow contains a precursor cell which has the potency to differentiate into muscle cells.