Studies have continued on the demonstration of the terminal complement complex, C5b-9, in fluids and tissues of patient with immunologically-medicated disease. Serum immune complexes, serum complement levels and serum C5b-9 levels were measured in a group of Sjogren's patients. Results in these assays were compared in patients with two distinct histopathologic types of inflammatory vascular disease, neutrophilic (hypocomplementemic) and mononuclear (normocomplementic). SC5b-9 was the most sensitive indicator of complement activation and was elevated in both forms of vasculitis, indicating that complement activation occurs with both histopathologic types. Levels of C3, C4, and Ch50 were lower in patients with neutrophilic than with mononuclear vascular disease. These results further extend the utility of using C5b-9 as an absolute indicator of complement activation, in situations where levels of individual complement components are normal. The results indicate that complement activation may play a role in both histopathologic forms of vasculitis in Sjogren's syndrome.