The immunoglobulin classes (Ig) /complement fixation (CF) of anti-dsDNA and immune complexes were studied in sera from 12 SLE patients with digital ulcer and/or gangrene. These immunological examinations were also done in sera from 41 SLE patients with other clinical manifestations of vasculitis including leg ulcer, livedo, thrombophlebitis, peripheral neuropathy, aseptic bone necrosis and Raynaud's phenomenon. The Ig classes and CF of anti-dsDNA in sera were assessed by Crithidia IF technique. The precipitation with polyethylene glycol and the C1q solid-phase enzyme immunoassay were used to detect circulating immune complexes. SLE patients with digital ulcer and/or gangrene had high titer and high positive rates of anti-dsDNA. IgG and IgA of anti-dsDNA were found to be significantly greater in the patients with digital ulcer and/or gangrene. The patients with digital ulcer and/or gangrene had also high titer of immune precipitates that included IgG and IgA. However, these patients had low incidences of CF of anti-dsDNA, low C1q binding activity, and nearly normal complement levels in sera. This result differed from the findings in active lupus nephritis. Almost all groups of clinical manifestations of vasculitis were normal or revealed high levels of complement in sera. Especially, in SLE patients with leg ulcer and livedo the complement in sera significantly increased more than that in sera from patients with other clinical manifestations of vasculitis.