CD5+ and CD23+ lymphocytes were determined in peripheral blood of patients with rheumatoid arthritis (RA) (n = 56), systemic lupus erythematosus (SLE) (n = 20) and primary Sjögren's syndrome (pSS) (n = 21). No definite correlation between the numbers of CD5+ or CD23+ cells and most of the parameters of disease activity was found. A significant correlation (r = 0.59, p = 0.005) between rheumatoid factor levels and numbers of CD23+ cells was found in RA patients not taking disease modifying agents. For SLE and pSS no signification associations with autoantibody production were found. In conclusion, although CD5+ and CD23+ B cells might be important in the pathogenesis of autoimmune diseases, determination of these subsets in peripheral blood of RA, SLE or pSS patients provides no clear useful clinical information for the individual patient.