Concomitant with their disease, autoimmune MRL-lpr/lpr mice develop a profound lymphadenopathy composed of an unusual dull Lyt-1+ population of T cells. To examine the unusual growth properties and origin of these T cells, as well as their potential role in disease, very rapidly growing T cell lines and clones have been developed from cultures of MRL-lpr/lpr spleen and LN cells. These were studied for growth receptors, oncogene expression, and surface markers. The results further demonstrate the unique nature of lpr-derived T cells and show that i) all lines and clones exhibit greatly elevated expression of both the c-myb and the c-raf oncogenes, ii) despite the reported defect in IL 2 receptor expression of mitogen-activated fresh MRL-lpr/lpr T cells, all long-term lines or clones bear large numbers of IL 2 receptors continuously and without stimulation, although iii) unlike slower growing IL 2-dependent lines from MRL-lpr/lpr mice, these rapidly growing lines and clones are poorly inhibited by anti-IL 2 receptor antibody. Such IL 2 receptor-bearing, nontransformated T cells that are easily maintained have been useful in growth factor studies.