The effect of recombinant interleukin-2 (IL-2) on proliferative and cytotoxic response of peripheral blood mononuclear cells (PBMC) was investigated in a group of 21 patients with systemic lupus erythematosus (SLE). There was a significant decrease in thymidine uptake of peripheral blood mononuclear cells when compared with controls. However, IL-2 induced cytotoxicity was not diminished and minimal frequencies of lymphokine-activated killer (LAK) cells precursors remained in the range of control group. These data provide an evidence about the dissection between proliferative and cytotoxic response of PBMCs to exogenous interleukin-2 in patients with SLE in vitro. The factors contributing to this effect and the clinical significance of these findings remains to be answered.