Serum levels of the soluble form of the interleukin-2 receptor (sIL-2R) were measured in the sera of 32 patients with systemic lupus erythematosus. A significant correlation was observed between the levels of sIL-2R and the SLAM score of disease activity (R:0.40; p: less than 0.05). The correlation was slightly lower than those between the SLAM score and the levels of anti-dsDNA or of the complement activity. The levels of sIL-2R were not significantly correlated with those of serum anti-ds-DNA and complement, nor with a sign of peripheral blood B cell hyperactivity, such as the spontaneous in vitro production of anti-DNA antibodies.