Selective growth of T lymphocytes occurred when unfractionated normal human bone marrow cells were cultured with conditioned medium obtained from phytohemagglutinin-stimulated normal human lymphocytes (Ly-CM). Cultures of up to 90 percent T cells have been maintained for more than 9 months. The T cells exhibited a strict growth dependence upon Ly-CM and were consistently negative for Epstein-Barr viral information.