Bullous pemphigoid is a subepidermal autoimmune blistering disease associated with autoantibodies to the hemidesmosomal bullous pemphigoid antigens 180 and 230. Most sera from bullous pemphigoid patients recognize epitopes within the N-terminal NC16A portion of the bullous pemphigoid 180 ectodomain. Using cryosections of human skin, patients' sera were shown to generate dermal-epidermal separation when coincubated with leukocytes and complement from healthy volunteers; however, the specificity of pathogenic autoantibodies in bullous pemphigoid patients has not yet been elucidated. In this study, by the use of a modified version of the cryosection model, we show that sera from all of 13 bullous pemphigoid patients and from two rabbits, immunized against bullous pemphigoid 180 NC16A, induced dermal-epidermal separation. This finding was confirmed with the use of IgG purified from patients' sera, whereas sera and purified IgG from healthy controls were not pathogenic. The induction of subepidermal splits in this experimental model was shown to be dependent on the presence of neutrophils, but not complement. Interestingly, patients' autoantibodies affinity purified against a recombinant form of bullous pemphigoid 180 NC16A retained their blister-inducing capacity, whereas patients' IgG depleted of reactivity to NC16A lost this ability. F(ab')2 fragments of antibodies specific to NC16A, lacking the Fc portion, did not induce splits. In addition, patients' autoantibodies purified against a recombinant fragment of the C-terminus of bullous pemphigoid 180 as well as rabbit antibodies to the intracellular portion of bullous pemphigoid 180 and to bullous pemphigoid 230 did not cause dermal-epidermal separation. Our in vitro results support the idea that autoantibodies to bullous pemphigoid 180 from patients with bullous pemphigoid are of pathogenic relevance.