The aim of this study was to evaluate an immunofluorescence skin test, the lupus band test (LBT), in comparison to other criteria as classified by the American Rheumatic Association for the diagnosis of systemic lupus erythematosus (SLE). Twenty patients with SLE and another 24 with different connective tissue diseases (rheumatoid arthritis 16, dermatomyositis 3, necrotizing vasculitis 5) were studied. Antinuclear antibodies (ANA) appeared very sensitive (100%) in the diagnosis of LES, though with a low specificity (63%). LBT was however both sensitive (80%) and specific (100%). Others ARA laboratory criteria (anti-dsDNA, anti-Sm, VDRL and hematological disorders) were also less sensitive and/or less specific than LBT. Most interestingly, LBT was positive in 7 SLE cases in which both dsDNA and Sm antibodies were negative. Thus, LBT appears a useful test in the diagnosis of SLE. In addition, it may be of critical value in certain subsets of patients in which the present ARA criteria may not suffice for diagnosis.