Knowledge of autoimmune bullous diseases has greatly increased with the recognition of new entities, and the use of the direct immunofluorescence (DIF) using 1 molar per liter of sodium chloride (1 M NaCl) treated skin has been proposed. To estimate the frequency with which the different DIF patterns are present, we performed a systematic study of the skin or oral mucosa samples in which linear deposits of IgG at the basement membrane zone were detected by routine DIF in the last 6 years. The DIF tests were done on 56 samples before and after splitting the epidermis from the dermis with 1M NaCl. In 40 biopsies (72%) IgG was found on either the epidermal side or on both sides after 1M NaCl split. These cases corresponded to bullous pemphigoid (n=33), herpes gestationis (n=5) and cicatricial pemphigoid (n=2). In 6 cases (10.7%), IgG deposits were observed only on the floor, five corresponding to bullous pemphigoid and one to bullous pemphigoid-like eruption induced by amoxicillin. Repeat direct immunofluorescence using 1M NaCl split skin indicates that at least 12% of patients who were initially diagnosed as bullous pemphigoid, may in fact suffer a different entity, requiring other techniques to achieve the right diagnosis. This test can be a useful routine screening for autoimmune bullous diseases.