the gingival basement membrane antigens, Type IV collagen, bullous pemphigoid antigen and epidermolysis bullosa acquisita antigen were studied by indirect immunofluorescence in 11 gingival specimens from patients with periodontitis and 2 normal gingival specimens. In the normal control gingival specimens, the antigens were all present and stained with a continuous linear pattern. In periodontitis, alterations occurred in the gingival basement membrane antigens in the apical portion of the pockets. These included thinning, interruptions, partial or complete absence involving one or more rete pegs and fragmentation. These alterations may result from the disease process or play a role in the pathogenesis.