Of 12 T-lymphoma cell lines investigated, one line, EL-4 azgr (Thy-1+, Lyt-1+, Lyt-2-3-,Ia-, T-200+, sIg-, and FcR-) and, to a lesser extent, the parental cell line, EL-4, produced T cell growth factor(s) (TCGF) when stimulated by the T-cell mitogen concanavalin A (Con A). Induced production of TCGF-E was detected by 6 h and maximal at 18-24 h. Purified TCGF-E from this source had an approximately 30,000 mol wt and the biological activity of TCGF produced by whole spleen cells, including: augmentation of T cell-mitogen responses, cytotoxic T lymphocyte (CTL) proliferation support dependence, augmented generation of CTL, lack of strain specificity, and failure to stimulate resting T cells. TCGF-E is neither synthesized or secreted by this lymphoma cell line unless stimulated by Con A. X-irradiation up to 7,000 rad failed to inhibit synthesis and secretion. These observations have a practical application in providing a relatively homogeneous clonal cell product for T cell culture support and for structural and functional studies of the TCGF molecule(s). They suggest also a model for examining mechanisms of triggering production and secretion of a regulatory molecule that controls T cell functions.