To investigate the possible correlation of levels of circulating anti-BP180 autoantibodies with disease activity in bullous pemphigoid (BP). Diagnostic study. Regional referral center at a university dermatology department. Fifteen patients with typical clinical, histologic, and immunofluorescence findings of BP who had not received prior systemic treatment. Initially, 6 consecutive patients with BP were treated with oral doxycycline and niacinamide. Subsequently, 9 consecutive patients with BP received a combination of oral dapsone and prednisolone. Disease activity, serum levels of autoantibodies to BP180, and titers of antibasement membrane zone autoantibodies were assayed before initiation of treatment and 4 and 8 weeks later. Reactivity to BP180 was analyzed by enzyme-linked immunosorbent assay using a recombinant form of BP180 NC16A. Titers of anti-basement membrane zone autoantibodies were assayed by indirect immunofluorescence on 1-mol/L sodium chloride-split human skin. In both treatment groups, disease activity correlated with serum levels of autoantibodies to BP180 NC16A (P = .004 [dapsone-prednisolone] and .007 [doxycycline-niacinamide]). No correlation was seen between disease activity and indirect immunofluorescence reactivity (P = .18 and .16, respectively). In patients receiving dapsone plus prednisolone, the dose of corticosteroids necessary to suppress new blister formation correlated with anti-BP180 reactivity (P = .002). In contrast to indirect immunofluorescence reactivity that reflects reactivity to both BP 180 and BP230, serum levels of autoantibodies to BP180 correlate with disease activity in BP. Assaying reactivity to BP180 should be a helpful guide for the therapeutic management of patients with this disease. Our results underline the pathogenic relevance of autoantibodies to human BP180.