Mice bearing the recessive gene lpr develop an age-dependent, massive lymphoproliferation, primarily in the lymph nodes (LN), with associated autoimmunity. LN cells from these mice express T cell receptor protein on the cell surface at 50-70% of normal levels. Normal levels of T cell receptor alpha, beta and gamma mRNA were found in these cells as compared to normal LN cells. Southern blot analysis of MRL-lpr/lpr LN DNA showed rearrangements in 80-90% of the chromosomes at the beta gene loci. The pattern of rearrangement indicated that a polyclonal rather than monoclonal expansion of T cells occurred. These data support a lymphokine-induction model of lymphoproliferation in MRL-lpr mice.