The hypothesis that autoimmune diseases might be due to a defect in immunoregulation was tested in systemic lupus erythematosus (SLE). We have applied the double immunofluorescence, flow cytometry technique to peripheral blood lymphocytes from patients with SLE. T cells were studied for their binding of the lectin Vicia villosa (VV) which is a phenotypic marker for contra-suppressor cells both in mice and humans. A significant increase in CD3+VV+ and CD8+VV+ cells was found in patients with SLE, as compared with age and sex matched controls (P less than 0.01). When the patients were divided according to the 'lupus activity criteria count', those with active disease had a significantly increased proportion of CD3+VV+ and CD8+VV+ cells, as compared with those showing no disease activity (P less than 0.001). Indeed, a sequential investigation showed that the proportion of CD8+VV+ cells changed in parallel with exacerbation and remission of disease activity. These results suggest that disease activity in SLE is associated with an increase in VV binding CD8 cells which can function as contrasuppressor cells.