Abstract
The concentration of C-reactive protein (CRP) in the sera of patients with systemic lupus erythematosus (SLE) was higher when the disease was active than when it was inactive, but was only markedly raised in patients suffering from identifiable microbial infection. CRP levels greater than 60 mg/l suggest the presence of intercurrent infection and may therefore be a valuable aid to the differential diagnosis of pyrexia in SLE.