In this study we assess the effect of ultraviolet radiation, exclusively within the UV-A1 (340-400 nm) range, on disease activity in SLE. Ten SLE patients were irradiated for 15 days, four of them then continuing treatment for 8 months, with low doses (60 kJ/m2/d) of UV-A1 irradiation. They were assessed clinically and serologically before, after 3 weeks, and after 8 months of therapy. Clinical indices of disease decreased in the 10 patients after 3 weeks by 39%; they decreased in the four patients irradiated for 8 months by 70%. Antibodies to Sjögren's syndrome A (anti-SSA) or antinuclear antibodies (ANA) decreased or disappeared in most patients. There were no side effects. In this uncontrolled study, UV-A1 irradiation appears to have been an effective and seemingly innocuous therapeutic modality for patients with SLE, decreasing signs and symptoms of disease, diminishing levels of autoantibodies and increasing in effectiveness with time.