Dermatitis herpetiformis (DH) is characterized by the granular deposition of IgA in the dermal papillary tips. The source and antigenic specificity of this IgA are unknown, largely because of the previous inability to isolate it for study. These granular IgA deposits, pathognomonic of DH, have been specifically isolated from 4-mm punch biopsies. Specific isolation was achieved by removing contaminating serum IgA by a combination of washes in saline and sodium dodecyl sulfate without a reducing agent present and mechanical isolation of papillary dermis. The tissue IgA was then solubilized by a buffer containing 1% sodium dodecyl sulfate and 0.2 mM dithiothreitol, a reducing agent. Immunoreactive alpha chains were recovered in eluates of DH skin in 6-fold greater amounts than in eluates of normal skin, coincident with disappearance of immunofluorescent-staining granular deposits of IgA. Extracted specific IgA was recovered in sufficient quantity for detection by immunoenzymatic stain, was partially composed of a native (165 Kd) molecular mass, and had alpha and kappa staining material, all indicating that the extracted immunoglobulin was in part intact.