Mucous membrane pemphigoid (MMP) is an autoimmune blistering disease frequently associated with scarring of involved clinical sites. At present, therapeutic intervention in the form of immunomodulating or immunosuppressive agents is often reserved until the onset of significant inflammation and/or early cicatrization. We have therefore studied the clinical and immunopathological findings in 67 patients with MMP in order to try to establish a reliable prognostic indicator by which patients at high risk may be identified early in the disease. Inclusion criteria were a predominantly mucosal disease and the detection of IgG and/or C3 anti-basement membrane zone (BMZ) immunoreactants using immunofluorescence techniques. Patients were allocated to three disease subgroups on the basis of the modality and duration of therapeutic intervention required to achieve effective control of disease. In addition, at presentation and at each follow-up visit, a clinical score for severity of involved clinical sites was awarded and serum collected for indirect immunofluorescence (IIF). A dual circulating anti-basement membrane zone (anti-BMZ) antibody response with IgG and IgA was significantly associated with a more severe and persistent disease profile (P < 0.001). The odds ratios for requiring systemic therapy were: 11.6 among patients in whom there was a clinical score > or = 5 compared with a score < 5, and 31.3 and 66.9 among patients with IgG alone and both IgG and IgA, respectively, compared with negative IIF. The findings suggest that an assessment based upon a combination of site severity score and the presence of circulating IgG and IgA by IIF using 1 mol/L salt-split human skin substrate may be considered a useful prognostic indicator.