To the Editor.— Serious side effects, including aseptic meningitis, were noted in several systemic lupus erythematosus (SLE) patients treated with ibuprofen (239:1062, 1978).1-3 We presently describe a specific cell-mediated immunity (CMI) to ibuprofen in SLE. The study group consisted of 11 women with SLE—two treated with ibuprofen, while the others never received this agent. Sixteen patients with active rheumatoid arthritis (RA) (five of them treated with ibuprofen) as well as ten healthy persons served as control subjects. In seven of the 11 SLE patients, the disease was active at the time of examination, as evidenced by high titers of antinuclear factor, anti-DNA antibodies, and low titers of C3 and C4 complement components. All but one patient were treated with antiinflammatory drugs, including aspirin, indomethacin, phenylbutazone, or corticosteroids. In the SLE patients treated with ibuprofen, 800 to 1,200 mg/day, maculopapular skin rashes developed on the trunk and extremities. Fever occurred