summaryHuman skin and mucous membranes were used to detect circulating auto‐antibodies by indirectimmunofluorescence in 20 patients with bullous pemphigoid and eight with cicatricial pemphigoid. The tissue substrate was used intact and after chemical separation through the basement membrane zone (BMZ) by incubation with i m NaCl. Chemically split skin and oral mucosa provided a more sensitive assay for demonstrating circulating anti BMZ antibodies. Use of a battery of substrates increased the number of positives in bullous pemphigoid from 30% detected on monkey oesophagus to 100% (tissue battery). In cicatricial pemphigoid there was an increase in the proportion of positive sera from 13% (monkey oesophagus) to 88% (tissue battery). In addition, a different class of antibody was frequently detected on split tissue substrate suggesting that new antigens are exposed by this procedur