We report the case of a patient with a widespread bullous skin disease and linear deposits of IgG and C3 at the dermal-epidermal junction using direct immunofluorescence microscopy. Indirect immunofluorescence analysis demonstrated circulating IgG autoantibodies that stained, like autoantibodies to laminin 5 and type VII collagen, the dermal side of 1 mol L−1 NaCl-split human skin. By immunoblotting dermal extracts, the patient's serum, like serum samples from two control patients, reacted with a 200-kDa protein. Using immunoelectron microscopy, the serum labelled a component of the lower lamina lucida, but not the lamina densa/sublamina densa region, distinguishing this from the type VII collagen localization pattern. By immunofluorescence microscopy on skin sections from patients lacking either laminin 5 (Herlitz's epidermolysis bullosa) or type VII collagen (recessive dystrophic epidermolysis bullosa of Hallopeau-Siemens), the patient's serum retained reactivity with these test substrates. The patient's disease responded rapidly to the use of topical corticosteroids and lesions healed without scarring or milia formation. Our results provide strong evidence for the hypothesis that the 200 kDa autoantigen is different from laminin 5 and type VII collagen. For this new disease, we propose the designation 'anti-p200 pemphigoid'.