The prevalence and antigen specificity of anti-neutrophil cytoplasmic antibodies (ANCA) in sera from 23 children with active systemic lupus erythematosus (SLE) were studied utilizing indirect immunofluorescence and IgG and IgM ELISA using crude neutrophil extract and purified proteinase 3, myeloperoxidase, lactoferrin, cathepsin G and elastase. ANCA were present in 69% of SLE children and consisted of IgM and IgG antibodies of variable specificities, but did not correlate with organ involvement or disease activity. It remains unclear whether they have pathogenic significance or are epiphenomena in the category of polyclonal B-cell activation. However, their presence is entirely compatible with SLE even though they have hitherto been commonly associated with other systemic vasculitides.