In 30 patients with systemic lupus erythematosus the number of a circulating basophils was countered in different stages of activity. An inverse correlation was found between the absolute basophils count and anti-DNA antibodies and presumptive circulating immune complexes (as judged by polyethylene glycol precipitation of serum). A positive correlation was found between the absolute basophil count and C3 or C4 levels. IgE on the basophil surface was determined by radioimmunoassay in 7 patients. All of them showed a significantly higher surface IgE number. When the count of circulating basophils was roughly normal, 5 out of the 6 patients showed a positive basophil degranulation test with native DNA. These results suggest the existence of an anti-DNA specific IgE in lupus patients. Depression of the circulating basophil count may be a useful index of lupus activity.